Glossary

Absolute	The micron rating of a filter. It indicates that any particle larger than a specific size will be trapped within the filter.
Absolute Filter Rating	Filter rating meaning that 99.9 % (or essentially all) of the particles larger than a specified micron rating will be trapped on or within the filter.
Absorption	The process in which one substance penetrates into the body of another substance, termed the absorbent. An example is the absorption of water into soil.
Acequia	Acequias are gravity-driven waterways, similar in concept to a flume. Most are simple ditches with dirt banks, but they can be lined with concrete. They were important forms of irrigation in the development of agriculture in the American Southwest. The proliferation of cotton, pecans and green chile as major agricultural staples owe their progress to the acequia system.
Acid	A substance which releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with a base to form a neutral salt and water. An acid is the opposite of an alkali, has a pH rating lower than 7.0, will turn litmus paper red, and has a sour taste. A substance that has a pH of less than 7, which is neutral. Specifically, an acid has more free hydrogen ions (H+) than hydroxyl ions (OH-).
Acid Aerosol	Very small liquid or solid particles that are acidic and are small enough to become airborne.
Acid Neutralizing Capacity	Measure of the buffering capacity of water; the ability of water to resist changes in pH.
Acid Rain	A broad term that includes any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms. This can include rain, snow, fog, hail or even dust that is acidic. Acid rain results when sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere and transported by wind and air currents. The SO2 and NOX react with water, oxygen and other chemicals to form sulfuric and nitric acids.
Acidic Deposition	The transfer of acidic or acidifying substances from the atmosphere to the surface of the Earth or to objects on its surface. Transfer can be either by wet-deposition processes (rain, snow, dew, fog, frost, hail) or by dry deposition (gases, aerosols, or fine to coarse particles).
Acidic Water	Water with a low pH, meaning that it's more likely to corrode metal pipes and leach metals out of exposed surfaces. Water that has a pH less than 6.5 could be acidic and corrosive. Acid water has the potential to leach metal ions, including iron, manganese, copper, lead, and zinc, from aquifers, plumbing fixtures, and piping. Because of its corrosive nature, this water could contain elevated levels of toxic metals, damage metal pipes. Many people also find that low pH water has a sour or metallic taste (because of the dissolved metals). It can also discolor laundry as well as plumbing fixtures.
Acidity	The quantitative capacity of a water or water solution to neutralize an alkali or base. It is usually measured by titration with a standard solution of sodium hydroxide, and expressed in ppm or mg/L of its calcium carbonate equivalent.
Acre	Foot (acre-ft.) - The volume of water needed to cover an acre of land to a depth of one foot; equivalent to 43,560 cubic feet or 325,851 gallons.
Acre-foot (acre-ft)	The volume of water required to cover 1 acre of land (43,560 square feet) to a depth of 1 foot. Equal to 325,851 gallons or 1,233 cubic meters.
Activated Alumina	A medium made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove several contaminants including fluoride, arsenic, and selenium. It requires periodic cleaning with a regenerant such as alum, acid and/or caustic.
Activated Carbon	A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous materials, such as coal, wood, or coconut shells, in the absence of air, creating a highly porous adsorbent material. Activated carbon is commonly used for dechlorination, organic chemical reduction and radon reduction, and is recognized by the US EPA as the best available technology for reduction of organic chemicals from drinking water.
Activated Coal	This is the most commonly used adsorption medium, produced by heating carbonaceous substances or cellulose bases in the absence of air. It has a very porous structure and is commonly used to remove organic matter and dissolved gases from water. Its appearance is similar to coal or peat. Available in granular, powder or block form; in powder form it has the highest adsorption capacity.
Activated Silica	A negatively charged colloidal substance generally formed by combining a dilute sodium silicate solution with a dilute acidic solution (or other activant). Generally used as a coagulant aid.
Activated Sludge	Oxygen dependent biological process that serves to convert soluble organic matter to solid biomass, that is removable by gravity or filtration.
Active Groups	Really fixed ions bolted on to the matrix of an ion exchanger. Each active group must always have a counter-ion of opposite charge near itself.
Adsorbate	Any substance that is or can be adsorbed. The liquid, gas or solid substance which is adsorbed as molecules, atoms, or ions.
Adsorbent	A water treatment medium, usually solid, capable of the adsorption of liquids, gases, and/or suspended matter. Activated alumina and activated carbon are common adsorbents used in water processing.
Adsorption	The physical process occurring when liquids, gases, or suspended matters adhere to the surfaces of, or in the pores of, an adsorbent media such as activated carbon. Adsorption is a physical process which occurs without chemical reaction.
Advanced Oxidation Process	One of several combination oxidation processes. Advanced chemical oxidation processes use (chemical) oxidants to reduce COD/BOD levels, and to remove both organic and oxidizable inorganic components. The processes can completely oxidize organic materials to carbon dioxide and water, although it is often not necessary to operate the processes to this level of treatment.
Advanced Wastewater Treatment	Any treatment of sewage water that includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids.
Advanced Water Treatment	The level of water treatment that requires an 85-percent reduction in pollutant concentration, also known as tertiary treatment.
Aerate	To supply air to water, soil, or other media.
Aerated Lagoon	A water treatment pond that speeds up biological decomposition of organic waste by stimulating the growth and activity of bacteria, which are responsible for the degradation.
Aeration	The process in which air is brought into intimate contact with water, often by spraying water through air, or by bubbling air through water. Aeration may be used to add oxygen to the water for the oxidation of matter such as iron, or to cause the release of dissolved gases such as carbon dioxide or hydrogen sulfide from the water.
Aeration Tank	A tank that is used to inject air into water.
Aerobic	An action or process conducted in the presence of air, such as aerobic digestion of organic matter by bacteria. Pertaining to, taking place in, or caused by the presence of oxygen.
Aerosol	Very small liquid or solid particles dispersed in air.
Affinity	The keenness with which an ion exchanger takes up and holds on to a counter-ion. Affinities are very much affected by the concentration of the electrolyte surrounding the ion exchanger.
Agglomeration	A process of bringing smaller particles together to form a larger mass.
Aggressive Water	Water that is soft and acidic and can corrode plumbing, pipes and appliances.
Air Check	A device which allows water, but not air, to pass through it. An air check is a typical component of a treatment system using a regenerant eductor.
Air Gap	A clear vertical space through the free atmosphere between the lowest opening of any pipe or faucet conveying water or waste to a tank, plumbing fixture receptor, or other device and the flood level rim of the receptacle. An air gap is used to prevent cross connection between a water treatment device and a possible source of wastewater thereby preventing a reverse flow of water from the sewer into the water supply system. Without an air gap, such reverse flow could occur due to an increase in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes usually require the air gap to be twice the diameter of the inlet with a minimum width of 1 1/2 inches.
Algae	Chlorophyll-bearing nonvascular, primarily aquatic species that have no true roots, stems, or leaves; most algae are microscopic, but some species can be as large asvascular plants.
Algal Bloom	The rapid proliferation of passively floating, simple plant life, such as blue-green algae, in and on a body of water.
Aliquot	A measured portion of a sample taken for analysis. One or more aliquots make up a sample.
Alkali	A substance which creates a bitter taste and a slippery feel when dissolved in water and will turn red litmus paper blue. An alkali has a pH greater than seven and is the opposite of an acid. Highly alkaline waters tend to cause drying of the skin. Alkalis may include the soluble hydroxide, carbonate, and bicarbonate salts of calcium, magnesium, potassium, and sodium. A hydroxide alkali may also be called a base.
Alkaline	Has a pH greater than 7; in common usage, a pH of water greater than 7.4. sometimes water or soils contain an amount of alkali (strongly basic) substances sufficient to raise the pH value above 7.0 and be harmful to the growth of crops.
Alkalinity	The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity. In the water industry, alkalinity is expressed in mg/l of equivalent calcium carbonate. There are three kinds of alkalinity: carbonate, bicarbonate, and hydroxide alkalinity. Total alkalinity is the sum of all three kinds of alkalinity. Different tests are used to determine the quantity of the different kinds of alkalinities present in water.
Alluvial Aquifer	A water-bearing deposit of unconsolidated material (sand and gravel) left behind by a river or other flowing water.
Alluvium	General term for sediments of gravel, sand, silt, clay, or other particulate rock material deposited by flowing water, usually in the beds of rivers and streams, on a flood plain, on a delta, or at the base of a mountain.
Alpine Snow Glade	A marshy clearing between slopes above the timberline in mountains.
Alternating System	As in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes usually require the air gap to be twice the diameter of the inlet with a minimum width of 1 1/2 inches.
Alum	The common name for aluminum sulfate [Al2 (SO4) x 14H2 O] which is often used as a coagulant in water treatment.
Amalgamation	The dissolving or blending of a metal (commonly gold and silver) in mercury to separate it from its parent material.
Ammonia	A compound of nitrogen and hydrogen (NH3) that is a common by-product of animal waste. Ammonia readily converts to nitrate in soils and streams.
Amoeba	A single celled protozoan that is widely found in fresh and salt water. Some types of amoebas cause diseases such as amoebic dysentery.
Anadromous Fish	Migratory species that are born in freshwater, live mostly in estuaries and ocean water, and return to freshwater to spawn.
Anaerobic	Pertaining to, taking place in, or caused by the absence of oxygen.
Anaerobic Organism	An organism that can thrive in the absence of oxygen (air), such as bacteria in a septic tank.
Angstrom Unit	A unit of wavelength of light equal to .00001 millimeter or .0001 microns.
Anion	A negatively charged ion in solution, such as bicarbonate, chloride, or sulfate. An anion [such as chloride (Cl-)] may result from the dissociation of a salt, acid, or alkali.
Anion Exchange	An ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger. In demineralization, for example, bicarbonate, chloride and sulfate anions are removed from solution in exchange for a chemically equivalent number of hydroxide anions from the anion exchange resin.
Anode	The positive pole of an electrolytic system. The metal which goes into solution in a galvanic cell. Anodes of metals such as magnesium and zinc are sometimes installed in water heaters or other tanks to deliberately establish galvanic cells to control corrosion of the tank through the sacrifice of the anode.
Anomalies	As related to fish, externally visible skin or subcutaneous disorders, including deformities, eroded fins, lesions, and tumors.
ANSI	Abbreviation for American National Standards Institute.
Anthropogenic	Having to do with or caused by humans.
Anticline	A fold in the Earth's crust, convex upward, whose core contains stratigraphically older rocks.
Appropriation Doctrine	The system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid west as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of First in Time, First in Right. The first person to take a quantity of water and put it to Beneficial Use has a higher priority of right than a subsequent user. Under drought conditions, higher priority users are satisfied before junior users receive water. Appropriative rights can be lost through nonuse; they can also be sold or transferred apart from the land. Contrasts with Riparian Water Rights.
Aquaculture	Farming of plants and animals that live in water, such as fish, shellfish, and algae.
Aquatic	Relating to water; living in or near water or taking place in surface water.
Aquatic Guidelines	Specific levels of water quality which, if reached, may adversely affect aquatic life. These are nonenforceable guidelines issued by a governmental agency or other institution.
Aqueduct	A pipe, conduit, or channel designed to transport water from a remote source, usually by gravity.
Aqueous	Of or containing water, typically as a solvent or medium.
Aqueous Solubility	The maximum concentration of a chemical that dissolves in a given amount of water.
Aquifer	SA body of permeable rock which can contain or transmit groundwater.
Aquifer (confined)	Soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.
Aquifer (unconfined)	An aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall.
Aromatics	A type of hydrocarbon that contains a ring structure, such as benzene and toluene. They can be found for instance in gasoline.
Arroyo	A small, deep, flat-floored channel or gully of anephemeralorintermittent stream, usually with nearly vertical banks cut, into unconsolidated material. A term commonly used in the arid and semiarid regions of the Southwestern United States.
Artesian	Describes underground water trapped under pressure between layers of impermeable rock. An artesian well is one that taps artesian water.
Artesian Water	Groundwater that is under pressure when tapped by a well and able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called artesian pressure, and the formation containing artesian water is an artesian aquifer or confined aquifer. See flowing well.
Artificial Recharge	A process where water is put back into groundwater storage from surface-water supplies such as irrigation, or induced infiltration from streams or wells.
ASME	Abbreviation for American Society of Mechanical Engineers.
Assimilation	The ability of water to purify itself of pollutants.
Assimilative Capacity	The capacity of natural water to receive wastewaters or toxic materials without negative effects and without damage to aquatic life or humans who consume the water.
Atmospheric Deposition	The transfer of substances from the air to the surface of the Earth, either in wet form (rain, fog, snow, dew, frost, hail) or in dry form (gases, aerosols, particles).
Atmospheric Pressure	The pressure exerted by the atmosphere on any surface beneath or within it; equal to 14.7 pounds per square inch at sea level.
Atom	The smallest unit of matter that is unique to a particular element. They are the ultimate building blocks for all matter.
Atomic Number	A specific number that differs for each element, equal to the number of protons in the nucleus of each of its atoms.
Attenuation	The process of reduction of a compound's concentration over time. This can be through absorption, adsorption, degradation, dilution or transformation.
Attrition	The action or process of gradually redusing the strength or effectiveness.
Automatic Water Softener (or Automatic Filter)	A water softener (or filter) that is equipped with a clock timer, meter, or sensor which automatically initiates the backwash and/or regeneration process at the preset intervals of time. A predetermined number of gallons of water usage or as determined by a sensor. All operations, including bypass of treated or untreated water (depending upon design), backwashing, brining, rinsing, and returning the unit to service are performed automatically.
Available Chlorine	A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials.
Average Discharge	As used by the U.S. Geological Survey, the arithmetic average of all complete water years of record of surface water discharge whether consecutive or not. The term average generally is reserved for average of record and mean is used for averages of shorter periods, namely, daily, monthly, or annual mean discharges.
AWWA	Abbreviation for American Water Works Association.

Back Pressure	Pressure which creates resistance against the flow of water.
Back Siphonage	Reverse seepage of water in a distribution system.
Backflow	Unwater flow of water in the reverse direction.
Backflow Preventor	A device or system installed in a water line to stop backflow from a non-potable source.
Background Concentration	A concentration of a substance in a particular environment that is indicative of minimal influence by human (anthropogenic) sources.
Backwash	Intentional backwards flow of water.
Backwater	A body of water in which the flow is slowed or turned back by an obstruction such as a bridge or dam, an opposing current, or the movement of the tide.
Bacteria	Unicellare microorganism which hasa cell wall but lacks organelles and an organized nucleus.
Bacterial Water Contamination	The introduction of unwanted bacteria into a water body.
Bacteriastatic	Having the ability to inhibit the growth of bacteria without destroying them. For example, silver impregnated activated carbon will limit bacterial colonization but not eliminate it.
Bactericide	Any substance or agent which kills bacteria.
Bank	The sloping ground that borders a stream and confines the water in the natural channel when the water level, or flow, is normal.
Bank Storage	The change in the amount of water stored in an aquifer adjacent to a surface-water body resulting from a change in stage of the surface-water body.
Bar	A unit of pressure. One bar equals 14.5 pounds per square inch (psi) or about 0.987 standard atmospheres.
Barrier Bar	An elongate offshore ridge, submerged at least at high tide, built up by the action of waves or currents.
Barrier Beach	A narrow, elongate sandy ridge rising slightly above the high-tide level and extending generally parallel with the mainland shore, separated from it by a lagoon.
Base	An alkali that releases hydroxyl ions when dissolved in water. Bases reset with acids to form a neutral salt and water. In general they taste bitter rather than sour, and feel slippery and reverse the color changes produced by acids in indicators. For example, they turn litmus paper blue. a substance that has a pH of more than 7, which is neutral. A base has less free hydrogen ions (H+) than hydroxyl ions (OH-).
Base Flow	Sustained flow of a stream in the absence of direct runoff. It includes natural and human-induced streamflows. Natural base flow is sustained largely by groundwater discharges.
Basic	The opposite of acidic; water that has a pH of greater than 7.
Basin and Range Physiography	A region characterized by a series of generally north-trending mountain ranges separated by alluvial valleys.
Batch Operation	The utilization of ion exchange resins to treat a solution in a container wherein the removal of ions is accomplished by agitation of the solution and subsequent decanting of the treated liquid.
Bed	A mass of ion exchange resin particles or filter media contained in a column.
Bed Depth	The height of the resin or filter media in the column after it has been properly conditioned for effective operation, usually expressed in inches. This depth excludes any supporting bed.
Bed Expansion	The effect produced during backwashing: the resin particles become separated and rise in the column. The expansion of the bed due to the increase of the space between resin particles may be controlled by regulating backwash flow.
Bed Material	Sediment composing the streambed.
Bed Sediment	The material that temporarily is stationary in the bottom of a stream or other watercourse.
Bedload	Particles in a flowing fluid, usually water, consists of particles that spend the majority of the time on the bottom, but are periodically entrained into the turbulent water flow and carried a short distance downstream before settling again.
Bedrock	The substructure composed of hard rock exposed or buried at the earth's surface.
Benthic Invertebrates	Insects, mollusks, crustaceans, worms, and other organisms without a backbone that live in, on, or near the bottom of lakes, streams, or oceans.
Benthic Organism	A form of aquatic life that lives on or near the bottom of streams, lakes, or oceans.
Benthic Zone	The lower region of a body of water including the bottom.
Best Management Practice (BMP)	An agricultural practice that has been determined to be an effective, practical means of preventing or reducingnonpoint-sourcepollution.
Bicarbonate Alkalinity	The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are procured, and the solution is alkaline.
Bicarbonates	Salts containing the anion HCO3-. When acid is added, this ion breaks into H2O and CO2, and acts as a buffer.
Bind	To exert a strong chemical attraction.
Binder	Chemicals that hold short fibers together in a cartridge filter.
Bioaccumulation	The increase in concentration of a substance in an organism over time.
Bioavailability	The capacity of a chemical constituent to be taken up by living organisms either through physical contact or by ingestion.
Biochemical	Refers to chemical processes that occur inside or are mediated by living organisms.
Biochemical Oxygen Demand (BOD)	The amount of oxygen, expressed in milligrams per liter, that is removed from aquatic environments by the life processes of micro-organisms.
Biochemical Process	A process characterized by, produced by, or involving chemical reactions in living organisms.
Biocide	A chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism.
Biodegradable	Subject to degradation into similar substances by biological action . Examples include detergents, sewage, and other organic matter by bacteria.
Biodegradable Pollutants	Pollutants that are capable of decomposing under natural conditions.
Biodegradation	Transformation of a substance into new compounds through biochemical reactions or the actions of microorganisms such as bacteria.
Biofilm	Population of various microorganisms, trapped in a layer of slime and excretion products, attached to a surface.
Biological Contaminants	Living organisms such as viruses, bacteria, fungi, and mammal and bird antigens that can cause harmful health effects to humans.
Biological Oxidation	Decomposition of complex organic materials by microorganisms through oxidation.
Biologically Activated Carbon	Activated carbon that supports active microbial growth, in order to aid in the degradation of organics that have been absorbed on its surface and in its pores.
Biomass	The amount of living matter, in the form of organisms, present in a particular habitat, usually expressed as weight-per-unit area.
Biomonitoring	The use of living organisms to test the suitability of effluents for discharge into receiving waters and to test the quality of such waters downstream from the discharge.
Bioremediation	The biological treatment of wastewater and sludge, by inducing the breakdown of organics and hydrocarbons to carbon dioxide and water.
Biota	The animals, plants, fungi, etc., of a region or period.
Biotransformation	Conversion of a substance into other compounds by organisms; including biodegradation.
Birm	The trade name for a manganese dioxide coated aluminum silicate used as an oxidizing catalyst filter medium for iron and manganese reduction.
Blackwater	Water that contains waste of humans, animals or food.
Blind spots	Any place on a filter medium where fluids cannot flow through.
Blinding	A build-up of particles in a filter medium, that prevents fluids from flowing through.
Blowdown	The withdrawal of water containing a high concentration of solids or dissolved solids or maintain a specified solids-to-water concentration ratio.
Blowout	A small saucer- or trough-shaped hollow or depression formed by wind erosion on a pre-existing dune or other sand deposit.
Blue	Baby syndrome- A condition most common in young infants and certain elderly people that can be caused by ingestion of high amounts of nitrate, which results in the blood losing its ability to effectively carry oxygen.
BOD	Biochemical Oxygen Demand; represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.
Bog	A nutrient-poor, acidic wetland dominated by a waterlogged, spongy mat of sphagum moss that ultimately forms a thick layer of acidic peat; generally, has no inflow or outflow; fed primarily by rain water.
Boiling Point	The temperature at which the vapor pressure of a liquid equals the pressure of its surface. The liquid will than vaporize If the pressure of the liquid varies, the actual boiling point varies. For water the boiling point is 100 degrees Celsius.
Bolson	An extensive, flat, saucer-shaped, alluvium-floored basin or depression, almost or completely surrounded by mountains and from which drainage has no surface outlet; a term used in the desert regions of the Southwestern United States.
Bone Char	A black pigment substance with a carbon content of about 10 percent, made by carbonizing animal bones. It is used as a selective anion exchanger for fluoride and arsenic reduction.
Boreal	A climatic zone having a definite winter with snow and a short summer that is generally hot, and which is characterized by a large annual range of temperature.
Bosque	A dense growth of trees and underbrush.
Bottled Water	Water that is sold in plastic containers for drinking water and/ or domestic use.
Bottom	Land forest- Low-lying forested wetland found along streams and rivers, usually on alluvial flood plains.
Brackish Water	Water with a salinity intermediate between seawater and freshwater (containing from 1,000 to 10,000 milligrams per liter of dissolved solids).
Braided Stream	A stream characterized by an interlacing or tangled network of several small branching and reuniting shallow channels.
Breakdown Product	A compound derived by chemical, biological, or physical action upon a pesticide. The breakdown is a natural process that may result in a more toxic or a less toxic compound and a more persistent or less persistent compound.
Breakpoint Chlorination	Addition of chlorine to water until there is enough chlorine present for disinfection of water.
Breakthrough	The first appearance in the solution flowing from an ion exchange unit of unabsorbed ions similar to those which are depleting the activity of the resin bed. Breakthrough is an indication that regeneration of the resin is necessary.
Brine	A high concentration solution of salt in water.
Brine Ejector (Eductor)	A device used to draw a solution such as brine from a storage tank and force it into a cation or anion water treatment unit.
Brine Tank	A tank which sits beside the softening unit and acts as a salt storage and brine supply.
Buffer	A solution that can resist pH change upon the addition of an acidic or basic components. It is able to neutralize small amounts of added acid or base, thus maintaining the pH of the solution relatively stable.
Bypass	A connection or a valve system that allows untreated water to flow to a water system while a softener or filter is being regenerated, backwashed or serviced; also applied to a special water line installed to provide untreated water to a particular tap, such as a sill cock.

Cake	Solid dewatered residue on a filter media after filtration.
Calcareous	A rock or substance formed of calcium carbonate or magnesium carbonate by biological deposition or inorganic precipitation, or containing those minerals in sufficient quantities to effervesce when treated with cold hydrochloric acid.
Calcite	Calcium carbonate (CaCO3). A trade name for finely ground limestone, very high in calcium carbonate, which is used to raise the pH of acidic water.
Calcium Carbonate Equivalent	All forms of water hardness and other salts are commonly expressed in terms of calcium carbonate equivalents. This is necessary so that minerals of varying weight can be expressed in chemically equivalent terms.
Calcium Hypo Chlorite	A chemical that is widely used for water disinfection, for instance in swimming pools or water purification plants. It is especially useful because it is a stable dry powder and can be made into tablets.
Calcium (Ca)	One of the primary elements of the earth's crust commonly found in water as a dissolved solid. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are means of clearly identifying hard water. It is sometimes referred to as lime.
Caldera	A large, more or less circular, basin-shaped volcanic depression whose diameter is many times greater than the volcanic vent.
Candle Filter	A relatively coarse aperture filter designed to retain a coat of filter medium on an extended surface.
Canopy Angle	Generally, a measure of the openness of a stream to sunlight. Specifically, the angle formed by an imaginary line from the highest structure (for example, tree, shrub, or bluff) on one bank to eye level at midchannel to the highest structure on the other bank.
Capacity	In a softener or deionizer it is the adsorption activity possessed in varying degree by ion exchange materials. This quality may be expressed as kilograins per cubic foot, gram-milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, etc., where the of these ratios represent the weight of the ions adsorbed and the denominators, the weight or volume of the adsorbent. It can also refer to the ability of any media to take up a specific contaminant and is rated by time over gallons. As to flow rates, it is the maximum or minimum flow obtainable under given conditions of media, temperature, pressure, velocity, etc.
Capillary Action	The ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity.
Capillary Fringe	The zone above the water table in which water is held by surface tension. Water in the capillary fringe is under a pressure less than atmospheric.
Capillary Membranes	Membranes about the thickness of a human hair, used for Reverse Osmosis, nanofiltration, ultrafiltration and microfiltration.
Capillary Zone	Soil area above the water table where water can rise up slightly through the cohesive force of capillary action.
Carbon Dioxide	Water with a low pH value usually contains free carbon dioxide. Its presence is caused generally by absorption of carbon dioxide (CO2) from the air as water falls as rain, or by decay of organic matter in the earth. Well water containing substantial quantities of CO2 has a resultant low pH and corrosive qualities. Carbon dioxide in water forms a weak carbonic acid.
Carbonaceous Exchangers	Ion exchange materials of limited capacity prepared by the sulfonation of coal, lignite, peat, etc.
Carbonate Hardness	Hardness of water caused by carbonate and bicarbonate by-products of calcium and magnesium.
Carbonate Rocks	Rocks (such as limestone or dolostone) that are composed primarily of minerals (such as calcite and dolomite) containing the carbonate ion (CO32-).
Carbonates	Chemical compounds related to carbon dioxide.
Carcinogen	Any substance or agent that tends to produce a cancer.
Cartridge Filter	Disposable filter device that has a filter range of 0.1 micron to 100 microns.
Catalysis	Chemical that increases the rate of a reaction but does not take a direct part in the reaction, so that it is still intact after the reaction has taken place.
Catch Basin	A sedimentation area designed to remove pollutants from runoff before being discharged into a stream or pond.
Cathode	A site in electrolysis where cations in solution are neutralized by electrons that plate out on the surface or produce a secondary reaction with water.
Cathodic Protection	The control of the electrolytic corrosion of an underground or underwater metallic structure by the application of an electric current is such a way that the structure is made to act as the cathode instead of anode of an electrolytic cell.
Cation	A positively charged particle or ion.
Caustic Soda	The common name for sodium hydroxide and often used as a regenerant of anion resin in deionization systems.
Center Pivot Irrigation	An automated sprinkler system involving a rotating pipe or boom that supplies water to a circular area of an agricultural field through sprinkler heads or nozzles.
Centrifugation	A separation process, which uses the action of centrifugal force to promote accelerated settling of particles in a solid-liquid mixture.
CFU	Colony Forming Units. This is a measure that indicates the number of microorganisms in water.
Channel Scour	Erosion by flowing water and sediment on a stream channel; results in removal of mud, silt, and sand on the outside curve of a stream bend and the bed material of a stream channel.
Channeling	The flow of water or regenerant taking the line of least resistance through a media bed, as opposed to the usual distributed flow through all passages of the bed. Channeling may be due to fouling of the bed, poor distribution design, low flow rates, or insufficient backwash.
Channelization	The straightening and deepening of a stream channel to permit the water to move faster or to drain a wet area for farming.
Check Valve	A valve that allows water to stream in one direction and will then close to prevent development of a back-flow.
Chelating Agents	Organic compounds that have the ability to draw ion from their water solutions into soluble complexes.
Chemical Feeder	A mechanical device designed to introduce chemicals into a water system, more or less accurately in proportion to water flow.
Chemical Oxidation	Process using hydrogen peroxide, ozone, combined ozone & peroxide, hypochlorite, Fenton's reagent, etc.
Chemical Oxygen Demand (COD)	The amount of matter, both organic and inorganic, in a water or wastewater which can be oxidized by boiling with a strong oxidizing acid, and expressed as the equivalent amount of oxygen. Often used as a membrane of the strength of sewage.
Chemical Pollution	Introduction of chemical contaminants into a water body.
Chemical Stability	Resistance to chemical change which ion exchange resins must posses despite contact with aggressive solutions.
Chemical Weathering	Dissolving of rock by exposure to rainwater, surface water, oxygen, and other gases in the atmosphere, and compounds secreted by organisms.
Chloramines	Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies.
Chlordane	Octachloro-4,7-methanotetrahydroindane. An organochlorine insecticide no longer registered for use in the U.S. Technical chlordane is a mixture in which the primary components are cis- and trans-chlordane, cis- and trans-nonachlor, and heptachlor.
Chlorinated Hydrocarbons	Hydrocarbons that contain chlorine. These include a class of persistent insecticides that accumulate in the aquatic food chain. Among them are DDT, aldrin, dieldrin, heptachlor, chlordane, lindane, endrin, Mirex, hexachloride, and toxaphene.
Chlorinated Solvent	Industrial chemicals used widely for metal cleaning and in production of thermoplastics, lacquers, perfumes and polyvinylchloride (PVC) products.
Chlorination	A water purification process in which chlorine is added to water for disinfection, for the control of present microorganisms. It is also used in the oxidation of compound impurities in water.
Chlorinator	A mechanical device specifically designed to feed chlorine gas or pellets, or solutions such as hypochlorides, into a water supply in proportion to the flow of water.
Chlorine	Widely used in the disinfection of water and as an oxidizing agent for organic matter, iron, hydrogen sulfide, etc. It is available as a gas, as a liquid in sodium, hypochlorite, or as a solid in calcium hypochlorite. In water chlorine reacts with organics to form trihalomethanes (THM) which can cause cancer.
Chlorine Contact Chamber	The part of a water treatment plant where effluent is disinfected by chlorine.
Chlorine Demand	A measure of the amount of chlorine which will be consumed by organic matter in a water before a chlorine residual will be found.
Chlorofluorocarbons	A class of volatile compounds consisting of carbon, chlorine, and fluorine. Commonly called freons, which have been in refrigeration mechanisms, as blowing agents in the fabrication of flexible and rigid foams, and, until banned from use several years ago, as propellants in spray cans.
Chrysene	Polycyclic aromatic hydrocarbon (PAH).
Cienaga	A marshy area where the ground is wet due to the presence of seepage or springs.
Circumneutral	Said of water with a pH between 5.5 and 7.4
Cirque	A deep, steep-walled, half-bowllike recess or hollow situated high on the side of a mountain and commonly at the head of a glacial valley; and produced by the erosive activity of mountain glaciers.
Clarity	The clearness of a liquid.
Clastic	Rock, such as sandstone, or sediment composed principally of broken fragments that are derived from preexisting rocks which have been transported from their place of origin.
Clay	Finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3 , MgO etc.) and organic matter.
Climate	The sum total of the meteorological elements that characterize the average and extreme conditions of the atmosphere over a long period of time at any one place or region of the Earth's surface.
Coagulant	A material such as alum, which will form a gelatinous precipitate in water, and gather finely divided particles into larger ones which can then be removed by settling and/or filtration.
Coagulation	Destabilization of colloid particles by addition of a reactive chemical, called a coagulant. This happens through neutralization of the charges.
Coalescence	Liquid particles in suspension that unite to create particles of a greater volume.
Coastal Zone	Lands and waters near the coast, whose uses and ecology are affected by the sea.
Code	Those regulations which the department having jurisdiction may lawfully adopt.
Coliform Bacteria	Commonly known as "indicator organisms", coliform refers to a wide variety of bacteria that can be found throughout the environment. This means that these organisms can be found in soil, water surfaces, vegetations as well as on the skin or intestinal tract of warm-blooded organisms such as humans.
Coliform Index	A rating of the purity of water based on a count of coliform bacteria.
Collector Sewers	Pipes to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility.
Colloid	Very finely divided solid particles larger than molecules but small enough that they will not settle out of a solution; intermediate between a dissolved particle and a suspended solid which will settle out of solution.
Color Throw	Discoloration of the liquid passing through a filtration or ion exchange media. It may be flushing from the media interstices of traces of colored organic reaction intermediates. It could indicate the presence of metallic ions, humus, tannins, or industrial wastes.
Combined Sewer	A sewer system that carries both sewage and rain water runoff.
Combined Sewer Overflow	A discharge of untreated sewage and stormwater to a stream when the capacity of a combined storm/sanitary sewer system is exceeded by storm runoff.
Commercial Water Use	Water used for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions. Water for commercial uses comes both from public-supplied sources, such as a county water department, and self-supplied sources, such as local wells.
Commercial Withdrawals	Water for use by motels, hotels, restaurants, office buildings, commercial facilities, and civilian and military institutions. The water may be obtained from a public supplier or it may be self-supplied.
Community	In ecology, the species that interact in a common area.
Compensated Hardness	A calculated value based on the hardness, the magnesium to calcium ratio, and the sodium concentration of a water. It is used to calculate the reduction in hardness removal capacity of a softener caused by these factors. No single method of calculation has been widely accepted.
Composite Sample	A series of water samples taken over a given period of time and weighted by flow rate.
Compounds	Two or more different elements held together in fixed proportions by attractive forces called chemical bonds.
Concentrate	The totality of different substances that are left behind in a filter medium after filtration.
Concentration	The measure of the amount of a sub-component (especially solute) in a solution.
Concentration Process	The process of increasing the number of particles per unit volume of a solution, usually by evaporating the liquid.
Condensate	A liquid formed by condensation.
Condensation	The process or the state of changing a substance from gas to liquid or solid.
Conductivity	The degree to which a specified material conducts electricity, calculated as the ratio of the current density in the material to the electric field that causes the flow of current.
Conduit	A natural or artificial channel through which fluids may be transported.
Cone of Depression	The depression of heads around a pumping well caused by withdrawal of water.
Confined Aquifer (artesian aquifer)	Anaquiferthat is completely filled with water under pressure and that is overlain by material that restricts the movement of water.
Confining Layer	A body of impermeable or distinctly less permeable material stratigraphically adjacent to one or more aquifers that restricts the movement of water into and out of the aquifers.
Confluence	The flowing together of two or more streams; the place where a tributary joins the main stream.
Conglomerate	A coarse-grained sedimentary rock composed of fragments larger than 2 millimeters in diameter.
Constituent	A chemical or biological substance in water, sediment, or biota that can be measured by an analytical method.
Consumptive Use	That part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Also referred to as water consumed.
Contact Recreation	Recreational activities, such as swimming and kayaking, in which contact with water is prolonged or intimate, and in which there is a likelihood of ingesting water.
Contact Time	The actual time which water remains in contact with an oxidizer, regenerant, or water conditioning media within a water treatment system.
Contaminant	Any foreign component in a substance, for example in water.
Contamination	Degradation of water quality compared to original or natural conditions due to human activity. The addition of any physical, chemical, biological or radiological substance to water which reduces the value of the water, or interferes with its intended use.
Contributing Area	The area in a drainage basin that contributes water to streamflow or recharge to an aquifer.
Conventional Sewer Systems	Systems that were traditionally used to collect municipal wastewater in gravity sewers and convey it to a central primary or secondary treatment plant, before discharge on receiving surface waters.
Conveyance Loss	The loss of water from a pipe or canal that is caused by leakage, seepage, evaporation, or evapotranspiration.
Cooling Tower	Large tower used to transfer the heat in cooling water from a power or industrial plant to the atmosphere either by direct evaporation or by convection and conduction.
Coral Reef	A ridge of limestone, composed chiefly of coral, coral sands, and solid limestone resulting from organic secretion of calcium carbonate; occur along continents and islands where the temperature is generally above 18°C.
Core Sample	A sample of rock, soil, or other material obtained by driving a hollow tube into the undisturbed medium and withdrawing it with its contained sample.
Corporation Cock	A stopcock screwed into the street water main to provide the house service connection.
Corrosion	The destructive disintegration of metals by electromechanical means. Corrosion of iron and steel is commonly called rusting.
Corrosivity	Ability of water to dissolve or break down certain substances, particularly metals.
Criterion	A standard rule or test on which a judgment or decision can be based.
Critical Bed Depth	The minimum depth of an adsorbent bed requited to contain the mass transfer zone.
Cross Connection	Any physical connection between two otherwise separated piping systems one of which contains potable water and the other of unknown or questionable safety, whereby flow may occur from one system to the other depending on the pressure differential between the two systems.
Cross Flow Filtration	A process that uses opposite flows across a membrane surface to minimize particle build-up.
Cross Linkage	The bonding of linear polymers into a resinous product with a material such as divenylbenzene (DVB). The degree of crosslinking is a factor of the resin's ability to withstand chemical oxidation. Softening resin is usually 8 percent crosslinked, but can range from 6 percent to 10 percent which is used in hot water applications.
Cryptosporidium	Microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as “Crypto.” There are many species of Cryptosporidium that infect animals, some of which also infect humans. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very tolerant to chlorine disinfection.
Crystalline Rocks	Rocks (igneous or metamorphic) consisting wholly of crystals or fragments of crystals.
CTA	Cellulose triacetate. Used to manufacture reverse osmosis membranes.
Cubic Foot Per Second (ft3/s, or cfs)	Rate of water discharge representing a volume of 1 cubic foot passing a given point during 1 second, equivalent to approximately 7.48 gallons per second or 448.8 gallons per minute or 0.02832 cubic meter per second. In a stream channel, a discharge of 1 cubic foot per second is equal to the discharge at a rectangular cross section, 1 foot wide and 1 foot deep, flowing at an average velocity of 1 foot per second.
Cultural Eutrophication	Decline of the oxygen rate in water, which has serious consequences for aquatic life, caused by humans.
Current	The portion of a stream or body of water, which is moving much faster than the rest of the water. The progress of the water is principally concentrated in the current.
Cycle	Recurrent series of events or processes in plants and animalsa life cycle; a growth cycle; a metabolic cycle.
Cyclone	An area of low pressure around which winds rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Cypress Dome	Small, isolated, circular, depressional, forested wetlands, in which cypress predominates, that have convex silhouettes when viewed from a distance.

Datum Plane	A horizontal plane to which ground elevations or water surface elevations are referenced.
DDT	Dichloro-diphenyl-trichloroethane. An organochlorine insecticide no longer registered for use in the United States.
De	Foaming agents-Chemicals that are added to wastewater discharges to prevent the water from foaming when it is discharged into a receiving water body.
De Alkalization	A process for the reduction of alkalinity in a water supply.
Deashing	The removal from solution of inorganic salts by means of adsorption by ion exchange resins of both the cations and the anions that comprise the salts.
Decant	To draw off the upper layer of liquid after the heaviest material (a solid or another liquid) has settled.
Decarbonation	The process of removing carbon dioxide from water, using contact towers or air scrubbers.
Dechlorination	The removal of excess or free chlorine from a water supply by adsorption with activated carbon or by catalytic type filter media.
Deciduous	Refers to plants that shed foliage at the end of the growing season.
Decomposition	The break down of organic matter by bacteria and fungi, to change the chemical structure and physical appearance of matter.
Decrosslinkage	The degradation of an ion exchange resin structure by destruction of the crosslink polymer as the result of aggressive attack by chlorine, ozone, hydrogen peroxide, or heat. Decrosslinking causes increased moisture content in an ion exchange resin and the physical swelling of the beads.
Deepwater Habitat	Permanently flooded lands lying below the deepwater boundary of wetlands.
Defluorination	The removal of fluoride from drinking water to prevent teeth damage.
Degasification	The process of removing dissolved gasses from water, using vacuum or heat.
Degassing	The removal of dissolved gasses from water such as carbon dioxide, methane, hydrogen sulfide, and oxygen. This can by done by subjecting the water to below atmospheric pressure, or by passing air through the water at atmospheric pressure.
Degradation Products	Compounds resulting from transformation of an organic substance through chemical, photochemical, and/or biochemical reactions.
Degraded	Condition of the quality of water that has been made unfit for some specified purpose.
Deionization	The removal of the ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure. First, positively charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. Second, negatively charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. The term is often used interchangeably with demineralization. The cation resin is regenerated with an acid and the anion resin is regenerated with sodium hydroxide (caustic soda).
Delta	The low, nearly flat tract of land at or near the mouth of a river, resulting from the accumulation of sediment supplied by the river in such quantities that it is not removed by tides, waves, or currents. Commonly a triangular or fan-shaped plain.
Delta P	The pressure drop or loss in psi between the inlet and the outlet of a water conditioner as the water flows.
Demi Water	Demineralized water. Water that is treated to be contaminant, mineral and salt free.
Demineralization	Processes to remove minerals from water, usually the term is restricted to ion exchange processes.
Denitrification	The process by which a nitrate becomes molecular nitrogen, especially by the action of bacteria.
Density	The weight of a certain amount of water. It is usually expressed in kilograms per cubic meter.
Density, Apparent (Density, Bulk)	The mass under specified conditions of a unit volume of a solid sorbent including its pore volume and inter-particle voids.
Depression Storage	The storage of water in low areas, such as ponds, and wetlands.
Depth Filtration	Treatment process in which the entire filter bed is used to trap insoluble and suspended particles in its voids as water flows through it.
Desalination	The removal of dissolved inorganic solids (salts) from a solution such as water to make it free of dissolved salts. Typically accomplished by reverse osmosis, distillation, or electrodialysis.
Desorption	The opposite of adsorption; the release of matter from the adsorption medium, usually to recover material.
Detect	To determine the presence of a compound.
Detection Limit	The concentration of a constituent or analyte below which a particular analytical method cannot determine, with a high degree of certainty, the concentration.
Detention Time	The actual time that a small amount of water is in a settling basin or flocculating basin. In storage reservoirs, it means the length of time water will be stored.
Detergent	Usually refers to synthetic detergent, but can be any material with cleansing powers such as soap, alkaline materials, synthetic detergents, solvents, and abrasives. Synthetic detergents are known as surfactants which foam and act like soap but are not made from fatty acids and lye.
Dewater	The separation of water from sludge, to produce a solid cake.
Dialysis	The separation of components of a solution by diffusion through a semi-permeable membrane which is capable of passing certain ions or molecules while rejecting others.
Diatoms	Single-celled, colonial, or filamentous algae with siliceous cell walls constructed of two overlapping parts.
Dieldrin	An organochlorine insecticide no longer registered for use in the United States. Also a degradation product of the insecticide aldrin.
Diffuser	A component of the ozone contacting system in an ozone generator that allows diffusion of an ozone containing gas.
Diffusion	The movement of gas molecules or aerosols into liquids, caused by a concentration gradient.
Digester	A closed tank for wastewater treatment, in which bacterial action is induced to break down organic matter.
Diluting Water	Distilled water that has been stabilized, buffered, and aerated. It is often applied in the BOD tests.
Direct Run Off	Water that flows over the ground surface directly into streams, rivers, or lakes. Also called storm runoff.
Discharge	The volume of water that passes a given location within a given period of time.
Discharge Area (ground water)	Area where subsurface water is discharged to the land surface, to surface water, or to the atmosphere.
Disinfectants	Fluids or gasses to disinfect filters, pipelines, systems, etc.
Disinfection	The decontamination of fluids and surfaces. To disinfect a fluid or surface a variety of techniques are used, such as ozone disinfection. Often disinfection means eliminating the present microorganisms with a biocide.
Dispersion	The extent to which a liquid substance introduced into a ground-water system spreads as it moves through the system.
Dissected	Cut by erosion into valleys, hills, and upland plains.
Dissolve	The process during which solid particles mix molecule by molecule with a liquid and appear to become part of the liquid.
Dissolved Air Flotation (DAF)	A procedure of induced flotation with very fine air bubbles or 'micro bubbles', of 40 to 70 microns.
Dissolved Constituent	Operationally defined as a constituent that passes through a 0.45-micrometer filter.
Dissolved Oxygen	The level of free oxygen present in water.
Dissolved Solids	Any minerals, salts, metals, cations or anions dissolved in water. Total dissolved solids (TDS) comprise inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates) and some small amounts of organic matter that are dissolved in water.
Distillation	Water treatment method where water is boiled to steam and condensed in a separate reservoir. Contaminants with higher boiling points than water do not vaporize and remain in the boiling flask.
Diversion	A turning aside or alteration of the natural course of a flow of water, normally considered physically to leave the natural channel. In some States, this can be a consumptive use direct from another stream, such as by livestock watering. In other States, a diversion must consist of such actions as taking water through a canal, pipe, or conduit.
Dolomite	A carbonate mineral of calcium and magnesium found in nature in extensive beds of compact limestone and marble that are rich in carbonate.
Domestic Water Use	Water used for household purposes, such as drinking, food preparation, bathing, washing clothes, dishes, and dogs, flushing toilets, and watering lawns and gardens. About 85% of domestic water is delivered to homes by a public-supply facility, such as a county water department. About 15% of the Nation's population supply their own water, mainly from wells.
Domestic Withdrawals	Water used for normal household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens. The water may be obtained from a public supplier or may be self-supplied. Also called residential water use.
Dominant Plant	The plant species controlling the environment.
Doppler Ultrasonic Meter	Doppler ultrasonic water meters use sound waves reflected off materials in the fluid, such as air bubbles or particulates, to measure flow velocity.
Drain Line	A pipe or conduit from a water conditioning unit used to carry backwash water, regeneration wastes and/or rinse water to a drain or waste system by gravity.
Drainage Area	The drainage area of a stream at a specified location is that area, measured in a horizontal plane, which is enclosed by a drainage divide.
Drainage Basin	Land area where precipitation runs off into streams, rivers, lakes, and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large drainage basins, like the area that drains into the Mississippi River contain thousands of smaller drainage basins. Also called a watershed.
Drainage Divide	Boundary between adjoining drainage basins.
Drawdown	The difference between the water level in a well before pumping and the water level in the well during pumping. Also, for flowing wells, the reduction of the pressure head as a result of the discharge of water.
Dredging	Cleaning, deepening, or widening of a waterway, using a machine (dredge) that removes materials by means of a scoop or a suction device.
Drinking	Water standard or guideline- A threshold concentration for a constituent or compound in a public drinking-water supply, designed to protect human health. As defined here, standards are U.S. Environmental Protection Agency regulations that specify the maximum contamination levels for public water systems required to protect the public welfare; guidelines have no regulatory status and are issued in an advisory capacity.
Drinking Water Standards	National Primary Drinking Water Standards are established by the U.S. Environmental Protection Agency (EPA) are health related and establish the maximum contaminant levels (MCL's) for regulated substances in drinking water. A MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer's tap. These standards relate to public water systems. National Secondary Drinking Water Standards are also issued by the EPA and pertain to aesthetic characteristics of water and are recommended only.
Drip Irrigation	An irrigation system in which water is applied directly to the root zone of plants by means of applicators (orifices, emitters, porous tubing, or perforated pipe) operated under low pressure. The applicators can be placed on or below the surface of the ground or can be suspended from supports.
Drought	A prolonged period of abnormally low rainfall, leading to a shortage of water.
Duplicates	Two separate samples with separate containers taken at the same time and at the same place.
DWV	Abbreviation for Drainage, Waste, and Vent. A name for copper or plastic tubing used for drain, waste, or venting pipes.
Dystrophic Lakes	Acidic bodies of water that contain many plants but few fish, due to the presence of great amounts of organic matter.

Ecological Studies	Studies of biological communities and habitat characteristicsto evaluate the effects of physical and chemical characteristics of water and hydrologic conditions on aquatic biota and to determine how biological and habitat characteristics differ among environmental settings.
Ecoregion	An area of similar climate, landform, soil, potential natural vegetation, hydrology, or other ecologically relevant variables.
Ecosystem	A community of organisms considered together with the nonliving factors of its environment.
Eductor	A venturi with an opening at the throat used to educt (suck in) air or liquid. The common method of introducing brine into a water softener.
Efficiency	The effectiveness of the operational performance of an ion exchanger. Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, e.g., pounds of acid per kilogram of salt removed.
Effluent	Outflow from a particular source, such as a stream that flows from a lake or liquid waste that flows from a factory or sewage-treatment plant. The outflow of a water treatment device. Sometimes used to mean the product water of a given water conditioning device or system.
Ejector	A device used to inject a chemical solution into wastewater during water treatment.
Electrical Charge	The charge on an ion, declared by its number of electrons. A Cl- ion is in fact a Cl atom which has acquired an electron, and a Ca++ ion is a Ca atom, which has lost two electrons.
Electrodialysis	The movement of ions is aided by an electric field applied across the semipermeable membrane.
Electrolysis	Process where electrical energy will change in chemical energy. The process happens in an electrolyte, a watery solution or a salt melting which gives the ions a possibility to transfer between two electrodes. The electrolyte is the connection between the two electrodes, which are also connected to a direct current. If you apply an electrical current, the positive ions migrate to the cathode while the negative ions will migrate to the anode. At the electrodes, the cations will be reduced, and the anions will be oxidized.
Electrolyte	A chemical compound that dissociates into ions and hence is capable of transporting electric charge.
Electromagnetic Meter	Electromagnetic (magmeter) meters use electromagnets to measure the water flow according to principles of fluid induction.
Electrons	Negatively charged building blocks of an atom that circle around the nucleus.
Elements	The distinctive building blocks of matter that make up every material substance.
Elution	The stripping of adsorbed ions from an ion exchange material by the use of solutions containing other ions in concentrations higher than those of the ions to be stripped. The process of washing out adsorbed material, especially by use of a solvent.
Elutriation	Freeing sludge of its mother liquor by washing it with water.
Emergent Plants	Erect, rooted, herbaceous plants that may be temporarily or permanently flooded at the base but do not tolerate prolonged inundation of the entire plant.
Emulsifier	A chemical that helps suspending one liquid in another.
Emulsion	Dispersion of one liquid in another liquid, occurs when a liquid in insoluble.
End	Point-The end point is that point in the exhaustion run of a water conditioner such as a softener or deionizer at which the water quality has dropped below an acceptable level
End of Pipe Techniques	Techniques for water purification that serve the reduction pollutants after they have formed.
Endangered Species	A species that is in imminent danger of becoming extinct.
Endocrine System	The collection of ductless glands in animals that secrete hormones, which influence growth, gender and sexual maturity.
Enrichment	When the addition of nutrients, such as nitrogen and phosphorus, from sewage effluent or agricultural runoff to surface water, greatly increases algal growth.
Environment	The sum of all conditions and influences affecting the life of organisms.
Environmental Framework	Natural and human-related features of the land and hydrologic system, such as geology, land use, and habitat, that provide a unifying framework for making comparative assessments of the factors that govern water-quality conditions.
Environmental Sample	A water sample collected from an aquifer or stream for the purpose of chemical, physical, or biological characterization of the sampled resource.
Environmental Setting	Land area characterized by a unique combination of natural and human-related factors, such as row-crop cultivation or glacial-till soils.
Ephemeral Stream	A stream or part of a stream that flows only in direct response to precipitation; it receives little or no water from springs, melting snow, or other sources; its channel is at all times above the water table.
EPT Richness Index	An index based on the sum of the number of taxa in three insect orders, Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies), that are composed primarily of species considered to be relatively intolerant to environmental alterations.
Equal	Width increment (EWI) sample- A composite sample of water collected across a section of stream with equal spacing between verticals and equal transit rates within each vertical that yields a representative sample of stream conditions.
Erosion	The geological process in which earthen materials are worn away and transported by natural forces such as wind or water.
Eschericha Coli (E. coli)	Coliform bacterium that is often associated with human and animal waste and is found in the intestinal court. It is used by health departments and private laboratories to measure the purity of water.
Estuarine Wetlands	Tidal wetlands in low-wave-energy environments where the salinity of the water is greater than 0.5 part per thousand and is variable owing to evaporation and the mixing of seawater and freshwater; tidal wetlands of coastal rivers and embayments, salty tidal marshes, mangrove swamps, and tidal flats.
Estuary	A partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.
Eutrophic	Referring to water that is rich in nutrients such as nitrogen and phosphorous.
Eutrophication	The process by which a body of water becomes enriched in dissolved nutrients (such as phosphates) that stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen.
Evaporation	The process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure.
Evaporation Ponds	Areas where sewage sludge is dumped and dried.
Evaporite Minerals (deposits)	Minerals or deposits of minerals formed by evaporation of water containing salts. These deposits are common in arid climates.
Evaporites	A class of sedimentary rocks composed primarily of minerals precipitated from a saline solution as a result of extensive or total evaporation of water.
Evapotranspiration	The sum of evaporation and plant transpiration from the Earth's land and ocean surface to the atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves.
Exchange Sites	Locations on ion exchange resin beads which hold mobile ions that are available for exchange with other ions in a solution passing through the bed. These sites are also called functional groups.
Exchange Velocity	The rate with which one ion is displaced from an exchanger in favor of another.
Exhaustion	The state of the adsorbent such as activated carbon, a water softener, or a deionizer that is no longer capable of the removal of a specific pollutant or of useful ion exchange. The exhaustion point is determined arbitrarily in terms of: (a) the presence or increase of an adsorbent contaminant as chlorine; (b) a value in parts per million of ions in the effluent solution; (c) the reduction in quality of the effluent water determined by a conductivity bridge which measures the resistance of the water to the flow of an electric current.
Exotic Species	Plants or animals not native to the area.

Facultative Bacteria	Bacteria that can live under aerobic or anaerobic conditions.
Fall Line	Imaginary line marking the boundary between the ancient, resistant crystalline rocks of the Piedmont province of the Appalachian Mountains, and the younger, softer sediments of the Atlantic Coastal Plain province in the Eastern United States. Along rivers, this line commonly is reflected by waterfalls.
Fallow	Cropland, tilled or untilled, allowed to lie idle during the whole or greater part of the growing season.
FDA Action Level	A regulatory level recommended by the U.S. Environmental Protection Agency for enforcement by the Food and Drug Administration (FDA) when pesticide residues occur in food commodities for reasons other than the direct application of the pesticide. Action levels are set for inadvertent pesticide residues resulting from previous legal use or accidental contamination. Applies to edible portions of fish and shellfish in interstate commerce.
Fecal Bacteria	Microscopic single-celled organisms (primarily fecal coliforms and fecal streptococci) found in the wastes of warm-blooded animals. Their presence in water is used to assess the sanitary quality of water for body-contact recreation or for consumption. Their presence indicates contamination by the wastes of warm-blooded animals and the possible presence of pathogenic (disease producing) organisms.
Fecal Coliform	See Fecal bacteria.
Fen	Peat-accumulating wetland that generally receives water from surface runoff and (or) seepage from mineral soils in addition to direct precipitation; generally alkaline; or slightly acid.
Fermentation	The conversion of organic matter to methane, carbon dioxide and other molecules by anaerobic bacteria.
Ferric Iron	Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide or ferric oxide (Fe2O3), which are suspended in water and visible as rusty water. Ferrous (iron in solution) is readily converted to ferric iron by exposure to oxygen found both in water and air. Ferric iron can by removed by filtration, but not by ion-exchange.
Ferrous Iron	Usually ferrous hydroxide which when dissolved in water produces a clear solution. Often called clear water iron, it can be removed by ion-exchange.
Fertilizer	Any of a large number of natural or synthetic materials, including manure and nitrogen, phosphorus, and potassium compounds, spread on or worked into soil to increase its fertility.
Filox R	A naturally occurring ore which serves as a catalytic filter media in the removal of iron, hydrogen sulfide and manganese. It normally requires only backwashing, but the use of oxidizers such as chlorine or potassium permanganate enhances its action.
Filter	A device used to clean water by removing iron, silt, taste, odor, color, etc., before it is fed into the softener or supply lines of the consumer. Includes mechanical, adsorptive, oxidizing and neutralizing filters. Available as media beds in tanks or as cartridge type devices
Filter Ag	The tradename for aluminum silicate (pumicite) granular product used as a general purpose filter medium. Lighter in weight, it requires a lower backwash rate. Typically removed suspended solids down to the 20-40 micron range.
Filter Medium	The permeable material that separates solids from liquids passing through it.
Filtrate	A gas or liquid that has been passed through a filter. fluid - a substance that is fluid at room temperature and pressure.
Filtration	A process used to separate solids from liquids or gases using a filter medium that allows the fluid to pass through but not the solid.
Fines	Smaller than the specified size or particles of ion exchange or filtration materials. An excess of fines can create undesirable pressure drop in the system.
First Draw	The water that comes out when a tap is first opened. It is likely that is has the highest level of lead contamination from weathering of pipelines.
Fission	Reproduction of microorganisms by means of cell division.
Fixture Count	A count of the total number of plumbing fixtures in a building to estimate peak flow rates and the sizing of equipment, especially for commercial buildings.
Fixture Unit	An arbitrary unit assigned to different type of plumbing fixtures, and used to estimate flow rate and drain capacity requirements.
Flash Distillation	A distillation process in which hot water is introduced into a low pressure chamber causing some of the water to flash or quickly turn to steam.
Floc	A flocculent mass that is formed in the accumulation of suspended particles. It can occur naturally but is usually induced in order to be able to remove certain particles from wastewater.
Flocculants	Materials added to water which can cause gelatinous clouds of precipitate to enclose fine particles of foreign material in order to settle or filter them from the water.
Flocculation	The accumulation of destabilized particles and micro flakes, and subsequently the formation of sizeable flakes. One must add another chemical called flocculent in order to facilitate the formation of flakes called flocs.
Flood	An overflow of water onto lands that are used or usable by man and not normally covered by water. Floods have two essential characteristics: The inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river, stream, lake, or ocean.
Flood Attenuation	A weakening or reduction in the force or intensity of a flood.
Flood Irrigation	The application of irrigation water whereby the entire surface of the soil is covered by ponded water.
Flood Plain	A strip of relatively flat land bordering a stream channel that is inundated at times of high water.
Flood Stage	The elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured.
Flood, 100-year	A 100-year flood does not refer to a flood that occurs once every 100 years, but to a flood level with a 1 percent chance of being equaled or exceeded in any given year.
Floodplain	The flat or nearly flat land along a river or stream that is covered by water during a flood.
Floodway	The channel of a river or stream and the parts of the floodplain adjoining the channel that are reasonably required to efficiently carry and discharge the flood water or flood flow of a river or stream.
Flotation	A solids-liquid or liquid-liquid separation procedure, which is applied to particles of which the density is lower than that of the liquid they are in. there are three types: natural, aided and induces flotation.
Flow	The discharge rate of a resource expressed in volume during a certain period of time.
Flow Augmentation	The addition of water to meet flow needs.
Flow Controller	An in-line self pressure adjusting or orifice to regulate the flow of water or regenerant through a water conditioner.
Flow Line	The idealized path followed by particles of water.
Flow Rate	The volume of solution which passes through a given quantity of resin within a given time. Flow rate is usually expressed in terms of gallons per minute per cubic foot of resin, or as milliliters per minute per milliliter of resin. If the flow rate is greater than it should be, the water will not be completely softened or filtered.
Flowing Well/Spring	A well or spring that taps groundwater under pressure so that water rises without pumping. If the water rises above the surface, it is known as a flowing well.
Flowpath	An underground route for ground-water movement, extending from a recharge (intake) zone to a discharge (output) zone such as a shallow stream.
Flush Valve (Flushometer)	A self closing valve used for flushing urinals and toilets. This type of valve allows flow rates of 15-20 gpm for up to 10 seconds.
Fluvial	Pertaining to a river or stream.
Fluvial Deposit	A sedimentary deposit consisting of material transported by suspension or laid down by a river or stream.
Flux	The product flow rate through a reverse osmosis, electrodialysis or ultrafiltration membrane. It is usually given in terms of volume unit per time per membrane area.
Flyway	A specific air route taken by birds during migration.
FM	Factory Mutual (FM) Approval is part of the FM Global Group and it is a testing and certification service. Products that pass the five-step approval process are issued the globally acknowledged FM mark to support property loss prevention and to signify that they will perform as expected.
Fouling	The deposition of organic matter on the membrane surface, which causes inefficiencies.
Fragmentation	The subdivision of a solid in fragments. The fragments will then adhere to the nearest surface.
Freeboard	The vertical distance between the static water level and the ceiling of an interceptor or water holding tank; the height above the static water level available for tank volume expansion during high flows. It may be expressed either as a linear distance or a percentage of bed depth.
Freezing	The change of a liquid into a solid as temperature decreases. For water, the freezing point is 0 degrees Celsius.
Freshwater	Water that contains less than 1,000 milligrams per liter (mg/L) of dissolved solids.
Freshwater Chronic Criteria	The highest concentration of a contaminant that freshwater aquatic organisms can be exposed to for an extended period of time (4 days) without adverse effects.See also Water-quality criteria.
Freshwater	Water that contains less than 1,000 milligrams per liter (mg/L) of dissolved solids; generally, more than 500 mg/L of dissolved solids is undesirable for drinking and many industrial uses.
Friable	Descriptive of a rock or mineral that crumbles naturally or is easily broken, pulverized, or reduced to powder.
Fumigant	A substance or mixture of substances that produces gas, vapor, fume, or smoke intended to destroy insects, bacteria, or rodents.
Furrow Irrigation	A type of surface irrigation whereby water is applied at the upper (higher) end of a field and flows in furrows to the lower end.

GAC	Granular Activated carbon.
Gage Height	The height of the water surface above the gage datum (zero point). Gage height is often used interchangeably with the more general term, stage, although gage height is more appropriate when used with a gage reading.
Gaging Station	A site on a stream, lake, reservoir or other body of water where observations and hydrologic data are obtained. The U.S. Geological Survey measures stream discharge at gaging stations.
Gallon	A common unit of liquid volume; the US gallon has a volume of 231 cubic inches or 3.78533 liters; the British (Imperial) gallon has a volume of 277.418 cubic inches or 4.54596 liters.
Galvanic Action	A form of corrosion which occurs when dissimilar metals in contact with each other and with an electrolyte causes on e of the metals to dissolve and go into solution. An example would be the result of connection copper to steel without an insulating (plastic) coupling or union. The anode metal with the higher electrode potential corrodes and the cathode is protected.
Geomorphic	Pertaining to the form or general configuration of the Earth or of its surface features.
Geomorphology	The science that treats the general configuration of the Earth's surface; the description of landforms.
Geothermal	Relating to the Earth's internal heat; commonly applied to springs or vents discharging hot water or steam.
Geyser	A geothermal feature of the Earth where there is an opening in the surface that contains superheated water that periodically erupts in a shower of water and steam.
Giardia	A microorganism that is commonly found in untreated surface water and can be removed by filtration. It is resistant to disinfectants such as chlorine.
Giardia Lamblia	A common protozoan found in water and is derived from animal droppings. It can cause contagious waterborne disease characterized by acute diarrhea. It is resistant to disinfectants such as chlorine, iodine, or ultraviolet light. Giardia can be removed by filters of four micron rating.
Giardiasis	A disease that results from an infection by the protozoan parasite Giardia Intestinalis, caused by drinking water that is either not filtered or not chlorinated. The disorder is more prevalent in children than in adults and is characterized by abdominal discomfort, nausea, and alternating constipation and diarrhea.
Glacial	Of or relating to the presence and activities of ice or glaciers.
Glacial Drift	A general term for rock material transported by glaciers or icebergs and deposited directly on land or in the sea.
Glacial Lake	A lake that derives its water, or much of its water, from the melting of glacial ice; also a lake that occupies a basin produced by glacial erosion.
Glacial Outwash	Stratified detritus (chiefly sand and gravel) washed out from a glacier by meltwater streams and deposited in front of or beyond the end moraine or the margin of an active glacier.
Glacier	A huge mass of ice, formed on land by the compaction and recrystallization of snow, that moves very slowly downslope or outward due to its own weight.
Grain (gr)	A unit of weight equal to 1/7000th of a pound or 0.0648 gram.
Grains Per Gallon (GPG)	An expression of concentration of material in solution. One grain per gallon is equivalent to 17.1 parts per million. This is the common reference for hardness of water.
Granite/Granitic Rock	A coarse-grained igneous rock.
Granular Activated Carbon	The heating of carbon to encourage active sites to absorb pollutants.
Gravel	Aggregate of more or less rounded rock fragments coarser than sand (i.e., more than 2 mm [0.08 inch] in diameter).
Gravel Support Bed	A layer or layers of graded gravel and course sand placed around and above the underdrain metalwork of a water treatment system. It facilitates even distribution and collection of both product water and backwash flow.
Gray Water	Domestic wastewater composed of wash water from kitchen, bathroom, and laundry sinks and from tubs, and washers.
Greensand	A natural mineral, primarily composed of complex silicates, which possess ion exchange properties. Greensand was the original material used in domestic and commercial water softeners and is the base product in the production of manganese greensand.
Greywater	Wastewater from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks.
Ground	Water flow system- The underground pathway by which ground water moves from areas of recharge to areas of discharge.
Groundwater	The term describing all subsurface water and the source of well water. It can be found in aquifers as deep as several miles.
Groundwater Discharge	Ground water entering coastal waters, which has been contaminated by land-fill leachates, deep well injection of hazardous wastes and septic tanks.
Groundwater Hydrology	The branch of hydrology that deals with the occurrence, movements, replenishment and depletion, properties and methods of investigation and utilization of groundwater.
Groundwater Recharge	Inflow of water to a groundwater reservoir from the surface. Infiltration of precipitation and its movement to the water table is one form of natural recharge. Also, the volume of water added by this process.
Groundwater, Confined	Groundwater under pressure significantly greater than atmospheric, with its upper limit the bottom of a bed with hydraulic conductivity distinctly lower than that of the material in which the confined water occurs.
Groundwater, Unconfined	Water in an aquifer that has a water table that is exposed to the atmosphere.
Growing Season	The frost-free period of the year.
Gully	A deeply eroded channel created by the concentrated flow of water.
Gypsum	A moderately insoluble calcium sulfate containing 20.9 percent water. It is often used to build soil structure and permeability.

Habitat	The part of the physical environment in which a plant or animal lives.
Half Life	The time required for a pollutant to lose one-half of its original concentration.
Halite	A geological term for rock salt, a mineral which is more than 95 percent sodium chloride. Also known as native or fossil salt.
Halogens	A family of elements that includes bromine, chlorine, fluorine, astatine, and iodine. They are very active chemically. They are commonly found as the ionic component in compounds with various other elements.
Hard Water	Hardness is caused by compounds of calcium and magnesium, and by a variety of other metals. General guidelines for classification of waters are: 0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard.
Hardness	A characteristic of natural water due to the presence of dissolved calcium and magnesium; water hardness is responsible for most scale formation in pipes and water heaters, and forms insoluble curd when it reacts with soaps. Hardness is usually expressed in grains per gallon, parts per million, or milligrams per liter, all as calcium carbonate equivalent. Temporary hardness, caused by the presence of magnesium of calcium bicarbonate, is so called because it may be removed by boiling the water to convert the bicarbonates to the insoluble carbonates. Calcium sulfate, magnesium sulfate, and the chlorides of these two metals cause permanent hardness.
Hardness Leakage	The presence in the effluent of the type of ions present in the water being treated. Leakage may be caused by incomplete regeneration, channeling, excessive service water, low temperature, high concentrations of sodium or interfering TDS in the feedwater.
Hardpan	A relatively hard,impervious, and usually clayey layer of soil lying at or just below land surface; produced as a result of cementation by precipitation of insoluble minerals.
Head Loss	The reduction on liquid pressure associated with the passage of a solution through a bed of exchange material; a measure of the resistance of a resin bed to the glow of the liquid passing through it.
Header	A central piping system with two or more side outlets located at the bottom of a water conditioning system. It's purpose is to both collect product water as well as to distribute backwash water.
Headwater(s)	(1) the source and upper reaches of a stream; also the upper reaches of a reservoir. (2) the water upstream from a structure or point on a stream. (3) the small streams that come together to form a river. Also may be thought of as any and all parts of a river basin except the mainstream river and main tributaries.
Health Advisory	Nonregulatory levels of contaminants in drinking water that may be used as guidance in the absence of regulatory limits. Advisories consist of estimates of concentrations that would result in no known or anticipated health effects (for carcinogens, a specified cancer risk) determined for a child or for an adult for various exposure periods.
Heat Exchanger	A component that is utilized to remove heat from or ad heat to a liquid.
Heavy Metals	Metals that have a density of 5.0 or higher and a high elemental weight. Most are toxic to humans, even in low concentrations.
Heavy Water	Water in which all the hydrogen atoms have been replaced by deuterium.
Heme Iron	Organically bound iron that can give water a pinkish cast. It is found only in groundwater supplies and cannot be removed by filtration. Like soluble iron, heme iron stains fixtures with a rust or orange coloring. It may draw clear and turn yellow or pink when exposed to oxygen.
Hemodialysis	The process of purifying a kidney patients blood by means of a dialysis membrane. In this process bodily waste is transferred from the blood into a hemodialysis grade water which is beyond the membrane.
Henry's Law	A way of calculating the solubility of a gas in a liquid, based on temperature and partial pressure, by means of constants.
Herbaceous	With characteristics of an herb; a plant with no persistent woody stem above ground.
Herbicide	A type of pesticide designed to kill plants.
Heterotrophic	Non-disease causing bacteria
Hexametaphosphate	A chemical, such as sodium hexametaphosphate, added to water to increase the solubility of certain ions and to inhibit precipitation of certain chemicals. Known as a sequestering agent, it forms a thin film that protects metals from corrosion.
Highly Saline Water	From 10,000 ppm to 35,000 ppm dissolved solids
Holding Pond	A pond or reservoir, usually made of earth, built to store polluted runoff.
Homeowner Water System	A water system that supplies piped water to a single residence.
Hot Lime (Soda Softening)	Partially softens water by adding lime and soda ash at a water temperature of about 212 degrees Fahrenheit. It chemically precipitates calcium, magnesium, iron, and silica. It also drives away carbon dioxide.
Human Health Advisory	Guidance provided by U.S. Environmental Protection Agency, State agencies or scientific organizations, in the absence of regulatory limits, to describe acceptable contaminant levels in drinking water or edible fish.
Humidification	The addition of water vapor to air.
Hydraulic Classification	The rearrangement of resin particles in an ion exchange unit. As the backwash water flows up through the resin bed, the particles are placed in a mobile condition wherein the larger particles settle and the smaller particles rise to the top of the bed.
Hydraulic Conductivity	Hydraulic conductivity is a measure of the ease with which water flows through sediments.
Hydraulic Gradient	The slope of the water table or potentiometric surface, that is, the change in water level per unit of distance along the direction of maximum head decrease.
Hydraulic Head	The height of the free surface of a body of water above a given point beneath the surface.
Hydric Soil	Soil that is wet long enough to periodically produceanaerobicconditions, thereby influencing the growth of plants.
Hydro Static Pressure	A measurement of structural strength and ability to hold water pressure. Hydrostatic pressure is more challenging to a system than air pressure because air will compress and absorb impact, whereas water will not.
Hydrocarbon	Organic compounds that are built of carbon and hydrogen atoms and are often used in petroleum industries.
Hydroelectric Power Water Use	The use of water in the generation of electricity at plants where the turbine generators are driven by falling water.
Hydrogen Cycle	A complete course of action exchange operation in which the cation medium is regenerated with acid and them all cations in the water are removed by exchange with hydrogen ions.
Hydrogen Sulfide (H2S)	A gas commonly found during the drilling and production of crude oil and natural gas, plus in wastewater treatment and utility facilities and sewers. The gas is produced as a result of the microbial breakdown of organic materials in the absence of oxygen. Colorless, flammable, poisonous and corrosive, H2S gas is noticeable by its rotten egg smell.
Hydrogeology	The science of chemistry and movement of groundwater.
Hydrograph	A graph showing the rate of flow versus time past a specific point in a river, channel, or conduit carrying flow.
Hydrologic Cycle	Cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff.
Hydrologic Regime	The characteristic behavior and total quantity of water involved in a drainage basin.
Hydrologic Unit	A geographic area representing part or all of a surface drainage basin or distinct hydrologic feature as delineated by the U. S. Geological Survey on State Hydrologic Unit Maps. Each hydrologic unit is assigned a hierarchical hydrologic unit code consisting of 2 digits for each successively smaller drainage basin unit.
Hydrology	The science that deals with water as it occurs in the atmosphere, on the surface of the ground, and underground.
Hydrolysis	The decomposition of organic compounds by interaction with water.
Hydrophilic	Having an affinity for water.
Hydrophobic	A molecule or part of a molecule with low polarity, usually characterized by few (if any) polar bonds and/or hydrogen bond acceptors and/or hydrogen bond donors. From Greek hydro (water) and phobos (fearing). Interchangeable with lipophilic, from Greek lipos (fat) and philia (bonding).
Hydrophyte	Any plant growing in water or on asubstratethat is at least periodically deficient in oxygen as a result of excessive water content.
Hydrosphere	Region that includes all the earth's liquid water, frozen water, floating ice, frozen upper layer of soil, and the small amounts of water vapor in the atmosphere.
Hydrostatic Pressure	The pressure exerted by the water at any given point in a body of water at rest.
Hydroxyl	The term used to describe the anionic hydroxide radical (OH-) which is responsible for the alkalinity of a solution.
Hypo Chlorite	An anion that forms products such as calcium and sodium hypo chlorite. These products are often used for disinfection and bleaching.
Hypoxic Waters	Waters with dissolved oxygen concentrations of less than 2 mg/L, the level generally accepted as the minimum required for life and reproduction of aquatic organisms.

Ice	The solid form of water.
Igneous Rocks	Rocks that have solidified from molten or partly molten material.
Imhoff Cone	A clear, cone-shaped container used to measure the volume of settle able solids in a specific volume of water.
Immiscibility	The inability of two or more solids or liquids to readily dissolve into one another.
Immobilize	To hold by a strong chemical attraction.
Impaired	Condition of the quality of water that has been adversely affected for a specific use by contamination or pollution.
Impermeability	The incapacity of a rock to transmit a fluid.
Impermeable	Not easily penetrated by water.
Impermeable Layer	A layer of solid material, such as rock or clay, which does not allow water to pass through.
Impervious	Impermeable.
Impurities	Particles or other objects that cause water to be unclear.
In Parallel Flow	A piping arrangement which directs separate streams through two or more water treatment units in a balanced manner, providing equal flow to each device. The inlets of two or more units are connected together and the outlets are connected together such that water will flow through the units simultaneously.
In Series Flow	A piping system in which all of the effluent flow of one unit in a water treatment system is fed to a second and succeeding unit. This arrangement achieves a greater reduction of contaminants than can be obtained by the passage through a single unit.
Index of Biotic Integrity (IBI)	An aggregated number, or index, based on several attributes or metrics of a fish community that provides an assessment of biological conditions.
Indicator	Any biological entity or process, or community whose characteristics show the presence of specific environmental conditions or pollutants.
Indicator Organisms	Microorganisms, such as coliforms, whose presence is indicative for pollution or for the presence more harmful microorganisms.
Indicator Sites	Stream sampling sites located at outlets of drainage basins with relatively homogeneous land use andphysiographicconditions.
Indicator Tests	Tests for a specific contaminant, group of contaminants, or constituent which signals the presence of something else.
Indirect Discharge	Introduction of pollutants from a non-domestic source into a publicly owned wastewater treatment system. Indirect dischargers can be commercial or industrial facilities whose wastes enter local sewers.
Indurated	Cemented, hardened, or a rocklike condition.
industrial Water Use	Water used for industrial purposes in such industries as steel, chemical, paper, and petroleum refining. Nationally, water for industrial uses comes mainly (80%) from self-supplied sources, such as a local wells or withdrawal points in a river, but some water comes from public-supplied sources, such as the county/city water department.
Industrial Withdrawals	Water withdrawn for or used for thermoelectric power (electric utility generation) and other industrial and manufacturing uses such as steel, chemical and allied products, paper and allied products, mining, and petroleum refining. The water may be obtained from a public supplier or may be self-supplied.
Infiltration	Groundwater that enters the sewer system through leaks in the pipe.
Influent	Fluid entering a treatment device.
Inhibitor	Chemical that interferes with a chemical reaction, such as precipitation.
Injection	The introduction of a chemical or medium into the process water to alter its chemistry or filter specific compounds.
Injection Well	Refers to a well constructed for the purpose of injecting treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into aquifers that don't deliver drinking water, unused aquifers, or below freshwater levels.
Inorganic	Containing no carbon; matter other than plant or animal.
Inorganic Chemicals	Chemical substances of mineral origin, not of basically carbon structure.
Inorganic Matter	Matter which is not derived from living organisms and contains no organically produced carbon; includes rocks, minerals and metals.
Inorganic Soil	Soil with less than 20 percent organic matter in the upper 16 inches.
Insecticide	A substance or mixture of substances intended to destroy or repel insects.
Instantaneous Discharge	The volume of water that passes a point at a particular instant of time.
Instream Use	Water use taking place within the stream channel for such purposes as hydroelectric power generation, navigation, water-quality improvement, fish propagation, and recreation.
Integrated Drainage	Drainage developed during geomorphic maturity in an arid region, characterized by coalescence of drainage basins as a result of headward erosion in the lower basins or spilling over from the upper basins.
Integrator or Mixed	Use site- Stream samplinglocated at an outlet of a drainage basin that contains multiple environmental settings. Most integrator sites are on major streams with relatively large drainage areas.
Interface	In hydrology, the contact zone between two fluids of different chemical or physical makeup.
Intermittent Stream	A stream that flows only when it receives water from rainfall runoff or springs, or from some surface source such as melting snow.
Intermontane	Situated between or surrounded by mountains, mountain ranges, or mountainous regions.
Internal Drainage	Surface drainage whereby the water does not reach the ocean, such as drainage toward the lowermost or central part of an interior basin or closed depression.
Intertidal	Alternately flooded and exposed by tides.
Intolerant Organisms	Organisms that are not adaptable to human alterations to the environment and thus decline in numbers where alterations occur.
Invertebrate	An animal having no backbone or spinal column.
Iodine Number	A measure of the ability of activated carbon to adsorb substances with low molecular weights. It is the milligrams of iodine that can be adsorbed on one gram of activated carbon.
Ion	An atom, or group of atoms in a solution which function as a unit, and has a positive or negative electrical charge, due to the gain or loss of one or more electrons. It is smaller than a colloid.
Ion Exchange	A reversible process in which ions are released from an insoluble permanent material in exchange for other ions in a surrounding solution; the direction of the exchange depends upon the affinities of the ion exchanger for the ions present and the concentration of the ions in the solution. The ion exchanger media is an insoluble permanent solid medium. for a product offering.
Ionization	The dissociation of molecules into simpler, electronically charged particles. It is related to the gaining or losing of electrons causing the atoms to become electronically charged.
Iron	An element often found dissolved in ground water (in the form of ferrous iron) in concentrations usually ranging from zero to 10 ppm (mg/l). It is objectionable in water supplies because of the staining caused after oxidation and precipitation (as ferric hydroxide), because of tastes, and because of unsightly colors produced when iron reacts with tannins in beverages such as coffee and tea. As little as 0.3 ppm of iron can cause staining. (See also ferrous iron, ferric iron, and heme iron).
Iron Bacteria	Organisms which are capable of utilizing ferrous iron, either from the water or from steel pipe, in their metabolism, and precipitating ferric hydroxide in their sheaths and gelatinous deposits. These organisms tend to collect in pipe lines and tanks during periods of low flow, and to break loose in slugs of turbid water to create staining, taste and odor problems.
Iron Fouling	The accumulation of iron on and within an ion exchange resin or filter bed resulting in a reduced capacity of the media.
Irrigation	The controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall.
Irrigation District	In the United States, a cooperative, self-governing public corporation set up as a subdivision of the state, with definite geographic boundaries, organized to obtain and distribute water for irrigation of lands within the district; created under authority of the State legislature with the consent of a designated fraction of the land owners or citizens and the taxing power.
Irrigation Return Flow	The part of irrigation applied to the surface that is not consumed byevapotranspirationor uptake by plants and that migrates to anaquiferor surface-water body.
Irrigation Water Use	Water application on lands to assist in the growing of crops and pastures or to maintain vegetative growth in recreational lands, such as parks and golf courses.
Irrigation Withdrawals	Withdrawals of water for application on land to assist in the growing of crops and pastures or to maintain recreational lands.

Jackson Turbidity Unit (JTU)	An arbitrary unit of turbidity originally based on a suspension of specific type of silica with the turbidity measured in a Jackson Candle Turbidimeter. This has been replaced by theÿnephelometric turbidity unit (NTU).
Jar Test	A laboratory test procedure with differing chemical doses, mix speeds, and settling times, to estimate the minimum or ideal coagulant dose required to achieve water quality goals.

Laboratory Water	Purified water used in the laboratory as a basis to create solutions or making dilutions. It contains no interfering substances.
Lacustrine	Pertaining to, produced by, or formed in a lake.
Lacustrine Wetlands	Wetlands within a lake or reservoir greater than 20 acres or within a lake or reservoir less than 20 acres if the water is greater than 2 meters deep in the deepest part of the basin; ocean-derived salinity is less than 0.5 part per thousand.
Lagoon	A stretch of salt water separated from the sea by a low sandbank or coral reef; Or an artificial pool for the treatment of effluent or to accommodate surface water that overflows drains during heavy rain.
Lake	An inland body of water, usually fresh water, formed by glaciers, river drainage, etc. It is usually larger than a pool or pond.
Laminar Flow	A flow in which rapid fluctuations are absent.
Land Application	Discharge of wastewater onto the ground for treatment or reuse.
Langelier Index (LI)	A calculated number that gives and indication of the tendency of water to form a protective film of calcium carbonate scale, to dissolve it or be in equilibrium with it. It does not take into account the quantities of film formed, the effect of velocities, oxygen, carbon dioxide, ammonia, silicon or natural inhibitors in the water.
Large Water System	A water system that services more than 50,000 customers.
Latent Heat	The amount of heat given up or absorbed when a substance changes from one state to another, such as from a liquid to a solid.
Lateral Moraine	A low ridgelike moraine carried on, or deposited near, the side margin of a mountain glacier.
Leach Field	Area where septic tank effluent is distributed by underground piping for natural leaching and percolation through the soil.
Leachate	Liquid that has percolated through a solid and leached out some of the constituents.
Leaching	The process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried away by wate.
Leakage	The phenomenon in which some of the influent ions are not adsorbed and appear in the effluent. It is usually caused by an under-regenerated exchange resin bed or by excessive flow rate.
Legionella	A series of bacteria, including legionella pneumophila, which can cause pneumonia-like illness called Legionnaires disease after the American Legion convention in Philadelphia where the disease first drew attention. These bacteria have been found growing in hard water scale and thrive below 140 degrees Fahrenheit in water heaters, showers, humidifiers, etc. Infection is obtained by inhalation.
Lentic Waters	Ponds or lakes (standing water).
Levee	A natural or manmade earthen barrier along the edge of a stream, lake, or river. Land alongside rivers can be protected from flooding by levees.
Life Zone	Major area of plant and animal life; region characterized by particular plants and animals and distinguished by temperature differences.
Light Absorption	The amount of light a certain amount of water can absorb over time.
Lime	The common name for calcium oxide (CaO); hydrated lime is calcium hydroxide, Ca(OH)2.
Lime Scale	Hard water scale containing a high percentage of calcium carbonate. Insoluble scale is commonly formed when water containing calcium carbonate is heated. It also forms in cold water but precipitates at a higher pH.
Lime Softening	Often used by municipalities for partial reduction of water hardness. After the addition of baked lime, soda ash is added to form an insoluble precipitate which is filtered from the water. This method leaves five or more grains of hardness.
Limestone	A sedimentary rockconsisting chiefly of calcium carbonate, primarily in the form of the mineral calcite.
Limnetic	The deepwater zone, greater than 2 meters deep.
Limnology	The study of the physical, chemical, hydrological, and biological aspects of fresh water.
Liquid	A state of matter, neither gas nor solid, that flows and takes the shape of its container.
Littoral	The shallow-water zone, less than 2 meters deep.
Livestock Water Use	Water used for livestock watering, feed lots, dairy operations, fish farming, and other on-farm needs.
Load	Material that is moved or carried by streams, reported as weight of material transported during a specified time period, such as tons per year.
Loess	A widespread, homogeneous, commonly nonstratified, porous,friable, slightly coherent, fine-grained blanket deposit of wind-blown and wind-deposited silt and fine sand.
Long	Term monitoring- The collection of data over a period of years or decades to assess changes in selected hydrologic conditions.
Lotic Waters	Flowing waters, as in streams and rivers.

Macroporous Resin	Ion exchange resins produced in both cation and anion versions with 12 percent or higher cross-linkage. They offer a higher resistance to oxidation and organic fouling.
Magnesium	One of the elements making up the earth's crust, the compounds of which when dissolved in water make the water hard. The presence of magnesium in water is a factor contributing to the formation of scale and insoluble soap curds.
Main Stem	The principal trunk of a river or a stream.
Major Ions	Constituents commonly present in water in concentrations exceeding 1.0 milligram per liter. Major cations are calcium, magnesium, sodium, and potassium; the major anions are sulfate, chloride, fluoride, nitrate, and those contributing to alkalinity, most generally assumed to be bicarbonate and carbonate.
Manganese Greensand	Greensand which has been processed to incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power, and is often used in the oxidation and precipitation of iron, manganese and/or hydrogen sulfide, and their removal from water. It is regenerated by the use of two to four ounces of a weak solution of potassium permanganate per cubic foot of manganese greensand.
Manganese (Mn)	A element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentrations. It causes black stains in laundry and plumbing fixtures at concentrations higher than 0.05 mg/l. It is removed the same way as iron, by ion-exchange or oxidation and filtration.
Marine Wetland	Wetlands that are exposed to waves and currents of the open ocean and to water having a salinity greater than 30 parts per thousand; present along the coastlines of the open ocean.
Marsh	A water-saturated, poorly drained area, intermittently or permanently water covered, having aquatic and grasslike vegetation.
Maturity	A stage in the evolutionary erosion of land areas in which the flat uplands have been widelydissectedby deep river valleys.
Maturity (stream)	The stage in the development of a stream at which it has reached its maximum efficiency, when velocity is just sufficient to carry the sediment delivered to it bytributaries; characterized by a broad, open, flat-floored valley having a moderate gradient and gentle slope.
Maximum Contaminant Level (MCL)	The designation given by the U.S. Environmental Protection Agency (EPA) to water-quality standards promulgated under the Safe Drinking Water Act. The MCL is the greatest amount of a contaminant that can be present in drinking water without causing a risk to human health.
MCL	Maximum Contaminant Level. A drinking water standard. The maximum amount of a contaminant allowed in drinking water.
MCLG	Maximum Contaminant Level Goal. The goal set for the maximum amount of a contaminant to be allowed in drinking water. Has not been approved to become the MCL.
Mean	The arithmatic average of a set of observations, unless otherwise specified.
Mean Discharge (MEAN)	The arithmetic mean of individual daily mean discharges of a stream during a specific period, usually daily, monthly, or annually.
Mean High Tide	The average altitude of all high tides recorded at a given place over a 19-year period.
Mean Low Tide	The average altitude of all low tides recorded at a given place over a 19-year period.
Mechanical Aeration	Use of mechanical energy to inject air into water to cause a waste stream to absorb oxygen.
Mechanical Filter	A filter primarily designed for the removal of suspended solid particles, as opposed to filters that remove contaminants by chemical means.
Mechanical Flotation	A term used in the mineral industry to describe the use of dispersed air to produce bubbles that measure 0.2 to 2 mm in diameter.
Media	Materials that form a barrier to the passage of certain suspended solids or dissolved liquids in filters.
Median	The middle or central value in a distribution of data ranked in order of magnitude. The median is also known as the 50th percentile.
Medium	Size water system-A water system that serves 3,300 to 50,000 customers.
Melting	The change of a solid into a liquid.
Membrane	A thin barrier that allows some compounds or liquids to pass through, and troubles others. It is a semi-permeable skin of which the pass-through is determined by size or special nature of the particles. Membranes are commonly used to separate substances.
Mesophyte	Any plant growing where moisture and aeration conditions lie between the extremes of wet and dry.
Mesotrophic	Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.
Metabolite	A substance produced in or by biological processes.
Metabolize	Conversion of food, for instance soluble organic matter, to cellular matter and gaseous by-products through a biological process.
Metamorphic Rocks	Rocks derived from preexisting rocks by mineralogical, chemical, or structural changes (essentially in a solid state) in response to marked changes in temperature, pressure, shearing stress, and chemical environment at depth in the Earth's crust.
Method Detection Limit	The minimum concentration of a substance that can be accurately identified and measured with current laboratory technologies.
MFS	Micro Filtration System, it serves full automatic solid/ liquid separation.
Microbial Growth	The multiplication of microorganisms such as bacteria, algae, diatoms, plankton, and fungi.
Micrograms Per Liter (æg/L)	A unit expressing the concentration of constituents in solution as weight (micrograms) of solute per unit volume (liter) of water; equivalent to one part per billion in most streamwater and ground water. One thousand micrograms per liter equals onemilligram per liter.
Microhm	One millionth of an ohm. A unit of measurement used to test the electrical resistance of water to determine its purity. The purer the water, the greater its resistance to conducting an electrical current. Water of absolute purity has a resistance of eighteen million ohms across one centimeter at a temperature of twenty-five degrees Celsius.
Micromho	One millionth of a mho. Used to measure the conductivity and the approximate TDS content of water. Absolute pure water has a conductivity of 0.055 micromhos per centimeter at 25 degrees Celsius. Also known as micro Siemens. The specific conductance is the reciprocal of resistance, therefore MHO is OHM spelled backwards.
Micron	A unit of length equal to one millionth of a meter, used in many technological and scientific fields.
Micron Rating	The term applied to a filter or filter medium to indicate the particle size above which all suspended solids will be removed, throughout the rated capacity. As used in industry standards, this is an absolute, not nominal rating.
Microorganisms	Organisms that are so small that they can only be observed through a microscope, for instance bacteria, fungi or yeasts.
Midge	A small fly in the family Chironomidae. The larval (juvenile) life stages are aquatic.
Milligram (mg)	One-thousandth of a gram.
Milligrams Per Liter (mg/l)	A measure of the concentration by weight of a substance per unit volume in water or wastewater. In reporting the results of water and wastewater analysis, mg/L is preferred to the unit parts per million (ppm), to which it is approximately equivalent.
Million Gallons Per Day (MGD)	A rate of flow of water equal to 133,680.56 cubic feet per day, or 1.5472 cubic feet per second, or 3.0689 acre-feet per day. A flow of one million gallons per day for one year equals 1,120 acre-feet (365 million gallons).
Mineral	A term applied to inorganic substances, such as rocks and similar matter found in the earth's strata, as opposed to organic substances such as plant and animal matter. Minerals normally have definite chemical composition and crystal structure. The term is also applied to matter derived from minerals, such as the inorganic ions found in water. The term has been incorrectly applied to ion exchangers, even though most of the modern materials are organic ion exchange resins.
Mineral Soil	Soil composed predominantly of mineral rather than organic materials; less than 20 percent organic material.
Mineral Water	Contains large amounts of dissolved minerals such as calcium, sodium, magnesium, and iron. Some tap waters contain as many or more minerals than some commercial mineral waters. There is no scientific evidence that either high or low mineral content water is beneficial to humans.
Minimum Reporting Level (MRL)	The smallest measured concentration of a constituent that may be reliably reported using a given analytical method. In many cases, the MRL is used when documentation for the method detection limit is not available.
Mining Water Use	Water use during quarrying rocks and extracting minerals from the land.
Miscibility	The ability of two liquids to mix.
Mist	Liquid particles measuring 40 to 500 micrometers, are formed by condensation of vapour. By comparison, fog particles are smaller than 40 micrometers.
Mitigation	Actions taken to avoid, reduce, or compensate for the effects of human-induced environmental damage.
Mixture	Various elements, compounds or both, that are mixed.
Moderately Saline Water	From 3,000 ppm to 10,000 ppm dissolved solids
Molecule	A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
Monitoring	Repeated observation, measurement, or sampling at a site, on a scheduled or event basis, for a particular purpose.
Monitoring Well	A well designed for measuring water levels and testing ground-water quality.
Monocyclic Aromatic Hydrocarbons	Single-ring aromatic compounds. Constituents of lead-free gasoline; also used in the manufacture of monomers and plasticizers in polymers.
Montane	Of, pertaining to, or inhabiting cool upland slopes below the timber line; characterized by the dominance of evergreen trees.
Moraine	A mound, ridge, or other distinct accumulation of unsorted, unstratified glacial drift, predominantlytill, deposited chiefly by direct action of glacier ice.
Mouth	The place where a stream discharges to a larger stream, a lake, or the sea.
Muck	Dark, finely divided, well-decomposed, organic matter forming a surface deposit in some poorly drained areas.
Municipal Discharge	Discharge of effluent from wastewater treatment plants, which receive wastewater from households, commercial establishments, and industries in the coastal drainage basin.
Municipal Sewage	Liquid wastes, originating from a community. They may have been composed of domestic wastewaters or industrial discharges.
Municipal Sludge	Semi liquid residue that remains from the treatment of municipal water and wastewater.
Municipal Water System	A water system that has at least five service connections or which regularly serves 25 individuals for 60 days; also called a public water system
Muskeg	Large expanses ofpeatlandsor bogs in subarctic zones.

Nanofiltration	A membrane process that treats water between reverse osmosis and ultrafiltration the filtration/separation spectrum. It can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color found in water. Nanofiltration may be used for selective removal of hardness ions.
National Geodetic Vertical Datum of 1929	NGVD 29 stands for National Geodetic Vertical Datum of 1929. It is a system that has been used by surveyors and engineers for most of the 20th Century. It has been the basis for relating ground and flood elevations, but it has been replaced by the moreaccurate North American Vertical Datum of 1988 (NAVD 88).
National Water	Quality Assessment (NAWQA) Program- The long term USGS program, begun in 1991, to assess the occurrence and distribution of water-quality conditions Nationwide.
Natural Levee	A long, broad, low ridge built by a stream on its flood plain along one or both banks of its channel in time of flood.
Navigable Water	In the context of the Clean Water Act, all surface water.
NEMA Enclosure Ratings	Terms like “waterproof,” “sealed,” “dust tight” and the like are used to describe electrical and electronic enclosures. Unfortunately, these terms are inherently ambiguous. Is the enclosure merely rain-proof or is it fully submersible? Is it sealed so that no air will transfer, or is it sealed against intrusion by objects? To clarify this situation with a clear set of standards, The National Electrical Manufacturer’s Association www.nema.org developed NEMA ratings. The ratings make it easy to specify enclosures with the right level of protection, however they can also be confusing. For example, NEMA 4 offers more stringent protection than NEMA 12. Many times engineers specify the wrong level of protection, either overspending or risking equipment damage. This guide will help you select the just-right NEMA rating for your application. Contact www.PARKUSA.com for more information.
NEMA 1 Enclosure Rating	For indoor use. Protects users against contact with hazardous components and protects the components from the ingress of solid objects, such as fingers and falling dirt.
NEMA 2 Enclosure Rating	Enclosures constructed for indoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); and to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing).
NEMA 3 Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.
NEMA 3R Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.
NEMA 3S Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and for which the external mechanism(s) remain operable when ice laden.
NEMA 3X Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); that provides an additional level of protection against corrosion and that will be undamaged by the external formation of ice on the enclosure.
NEMA 3RX Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); that will be undamaged by the external formation of ice on the enclosure that provides an additional level of protection against corrosion; and that will be undamaged by the external formation of ice on the enclosure.
NEMA 3SX Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); that provides an additional level of protection against corrosion; and for which the external mechanism(s) remain operable when ice laden.
NEMA 4 Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow, splashing water, and hose directed water); and that will be undamaged by the external formation of ice on the enclosure.
NEMA 4X Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow, splashing water, and hose directed water); that provides an additional level of protection against corrosion; and that will be undamaged by the external formation of ice on the enclosure.
NEMA 5 Enclosure Rating	Enclosures constructed for indoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and settling airborne dust, lint, fibers, and flyings); and to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing).
NEMA 6 Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (hose directed water and the entry of water during occasional temporary submersion at a limited depth); and that will be undamaged by the external formation of ice on the enclosure.
NEMA 6P Enclosure Rating	Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (hose directed water and the entry of water during prolonged submersion at a limited depth); that provides an additional level of protection against corrosion and that will be undamaged by the external formation of ice on the enclosure.
NEMA 7 Enclosure Rating	Enclosure used in Hazardous Locations, when completely and properly installed and maintained. Enclosures constructed for indoor use in hazardous (classified) locations classified as Class I, Division 1, Groups A, B, C, or D as defined in NFPA 70. Designed to contain an internal explosion without causing an external hazard.
NEMA 8 Enclosure Rating	Enclosure used in Hazardous Locations, when completely and properly installed and maintained. Enclosures constructed for either indoor or outdoor use in hazardous (classified) locations classified as Class I, Division 1, Groups A, B, C, and D as defined in NFPA 70. Designed to prevent combustion through the use of oil-immersed equipment.
NEMA 9 Enclosure Rating	Enclosure used in Hazardous Locations, when completely and properly installed and maintained. Enclosures constructed for indoor use in hazardous (classified) locations classified as Class II, Division 1, Groups E, F, or G as defined in NFPA 70. designed to prevent the ignition of combustible dust.
NEMA 10 Enclosure Rating	Enclosure used in Hazardous Locations, when completely and properly installed and maintained. Enclosures constructed to meet the requirements of the Mine Safety and Health Administration, 30 CFR, Part 18. Designed to contain an internal explosion without causing an external hazard.
NEMA 12 Enclosure Rating	Enclosures constructed (without knockouts) for indoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and circulating dust, lint, fibers, and flyings); and to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing).
NEMA 12K Enclosure Rating	Enclosures constructed (with knockouts) for indoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and circulating dust, lint, fibers, and flyings); and to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing).
NEMA 13 Enclosure Rating	Enclosures constructed for indoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and circulating dust, lint, fibers, and flyings); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing); and to provide a degree of protection against the spraying, splashing, and seepage of oil and non-corrosive coolants.
Explosion-Proof Enclosure	Explosion-proof does not mean the absence of explosions. Rather, an explosion-proof enclosure prevents any generated flames, sparks, or hot gases from escaping. How? A typical explosion-proof system has extended threaded flanges that provide a long flame path, which serves to cool, control, and contain the ignition. See NEMA 7, 8, 9, 10 Enclosure Rating
Intrinsically Safe	Intrinsically safe equipment is defined as "equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture in its most easily ignited concentration." This is achieved by limiting the amount of power available to the electrical equipment in the hazardous area to a level below that which will ignite the gases.
Nephelometric Turbidity Unit (NTU)	The standard unit of measurement used to measure turbidity in water. It makes use of a light scattering effect of fine suspended particles in a light beam. The NTU has replaced the Jackson Turbidity Unit (JTU) as the standard of measurement.
Neutralization	The addition of substances to neutralize water, so that it is neither acid, nor basic. Neutralization does not specifically mean a pH of 7.0, it just means the equivalent point of an acid-base reaction.
Neutralizer	A common designation for alkaline materials such as calcite (calcium carbonate) or magnesia (magnesium oxide) used in the neutralization of acid waters. Alkaline water can also be neutralized by the addition of an acid. The neutral point of the pH scale is 7.0, indicating the presence of equal numbers of free hydrogen and hydroxide ions.
Neutrons	Uncharged building blocks of an atom that play a part in radio-activity. They can be found in the nucleus.
Nitrate	An ion consisting of nitrogen and oxygen (NO3-). Nitrate is a plant nutrient and is very mobile in soils.
Nitrification	A biological process, during which nitrifying bacteria convert toxic ammonia to less harmful nitrate. It is commonly used to remove nitrogen substances from wastewater, but in lakes and ponds it occurs naturally.
Non	Expressing negation or absence.
Noncontact Water Recreation	Recreational activities, such as fishing or boating, that do not include direct contact with the water.
Nonpersistent Emergent Plants	Emergent plants whose leaves and stems break down at the end of the growing season from decay or by the physical forces of waves and ice; at certain seasons, there are no visible traces of the plants above the surface of the water.
Nonpoint	Source contaminant- A substance that pollutes or degrades water that comes from lawn or cropland runoff, the atmosphere, roadways, and other diffuse sources.
Nonpoint Source	A source (of any water-carried material) from a broad area, rather than from discrete points.
Non-point Source (NPS) Pollution	Pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides.
Nonselective Herbicide	Kills or significantly retards growth of most higher plant species.
NSF	Abbreviation for National Sanitation Foundation Testing Laboratory
Nucleus	The center of an atom, that contains protons and neutrons and carries a positive charge.
Nuisance Contaminant	Constituents in water, which are not normally harmful to health but may cause offensive taste, odor, color, corrosion, foaming, or staining.
Nuisance Species	Undesirable plants and animals, commonlyexoticspecies.
Nutrient	A substance that provides nourishment essential for growth and the maintenance of life.
Nutrient Pollution	Contamination of water resources by excessive inputs of nutrients. In surface waters, excess algal production is a major concern.

Offstream Use	Water withdrawn or diverted from a ground- or surface-water source for use.
Ohm	A unit of measure determining the resistance to passage of an electrical current. In a solution, it is related to the electrolyte concentration in the solution.
Oligotrophic Lakes	Deep clear lakes with few nutrients, little organic matter and a high dissolved-oxygen level.
Operating Pressure	The range of pressure, usually expressed in pounds per square inch, over which a water conditioning device or water system is designed to function. Usually 30-100 psi.
Organic	Containing carbon, but possibly also containing hydrogen, oxygen, chlorine, nitrogen, and other elements.
Organic Detritus	Any loose organic material in streams - such as leaves, bark, or twigs - removed and transported by mechanical means, such as disintegration or abrasion.
Organic Matter	Plant and animal residues, or substances made by living organisms. All are based upon carbon compounds.
Organic Soil	Soil that contains more than 20 percent organic matter in the upper 16 inches.
Organics (i.e.,Organic Chemicals)	Term used to describe any or all of the compounds with chemical structures based on carbon. Examples are hydrocarbons, wood, sugars, proteins, methane, petroleum-based compounds, solvents, pesticides, herbicides, trihalomethane (THM) and trichloroethylene (TCE).
Organochlorine Compound	Synthetic organic compounds containing chlorine. As generally used, term refers to compounds containing mostly or exclusively carbon, hydrogen, and chlorine. Examples include organochlorine insecticides, polychlorinated biphenyls, and some solvents containing chlorine.
Organochlorine Insecticide	A class of organic insecticides containing a high percentage of chlorine. Includes dichlorodiphenylethanes (such as DDT), chlorinated cyclodienes (such as chlordane), and chlorinated benzenes (such as lindane). Most organochlorine insecticides were banned from use in the United States because of their carcinogenicity, tendency to bioaccumulate, and toxicity to wildlife.
Organochlorine Pesticide	See Organochlorine insecticide.
Organonitrogen Herbicides	A group of herbicides consisting of a nitrogen ring with associated functional groups and including such classes as triazines and acetanilides. Examples include atrazine, cyanazine, alachlor, and metolachlor.
Organophosphate Insecticides	A class of insecticides derived from phosphoric acid. They tend to have high acute toxicity to vertebrates. Although readily metabolized by vertebrates, some metabolic products are more toxic than the parent compound.
Organophosphorus Insecticides	Insecticides derived from phosphoric acid and generally the most toxic of all pesticides to vertebrate animals.
Orographic	Pertaining to mountains, in regard to their location and distribution; said of the precipitation caused by the lifting of moisture-laden air over mountains.
Osmosis	The movement of water molecules through a thin membrane.
Osmotic Pressure	The pressure and potential energy difference that exists between solutions on either side of a semi-permeable membrane. This pressure is caused by the tendency of water to flow in osmosis. Every 100 ppm (mg/L) of TDS produces about one pound per square inch of osmotic pressure. Osmotic pressure must first be overcome by water pressure in the reverse osmosis process.
Outfall	The place where a sewer, drain, or stream discharges; the outlet or structure through which reclaimed water or treated effluent is finally discharged to a receiving water body.
Outwash	Soil material washed down a hillside by rainwater and deposited upon more gently sloping land.
Overflow Rate	One of the guidelines for design of the settling tanks and clarifiers in a treatment plant to determine if tanks and clarifiers are used enough.
Overland Flow	The flow of rainwater or snow melt over the land surface toward stream channels.
Oxalic Acid	Can be used for the removal of iron stains from most washable fabrics. Oxalic acid crystals can be obtained at most drug stores. It is poisonous and a skin irritant, therefore precautions must be used.
Oxbow	A bow-shaped lake formed in an abandoned meander of a river.
Oxidation	A chemical process in which electrons are removed from an atom, ion or compound. The addition of oxygen is a speciform of oxidation. Combustion is an extremely rapid form of oxidation, while the rusting of iron is a slow form.
Oxidation Pond	A man-made body of water in which waste is consumed by bacteria.
Oxidizing Agent	A chemical substance that brings about the oxidation of other substances in chemical oxidation and reduction reactions. Examples of oxidizing agents include oxygen, ozone, chlorine and peroxide.
Oxidizing Filter	A type of filter used to change the valence state of dissolved molecules, making them insoluble and therefore filterable. For example, a filter that oxidizes ferrous iron, manganous manganese, and/or anionic sulfur by use of a catalytic media such as manganese oxide and then filters the oxidized precipitant out of the water.
Oxygen Demand	The need for molecular oxygen to meet the needs of biological and chemical processes in water. Even though very little oxygen will dissolve in water, it is extremely important in biological and chemical processes.
Oxygen Depletion	The reduction of the dissolved oxygen level in a water body.
Ozone	An unstable form of oxygen (03), which can be generated by sending a high voltage electrical discharge through air or regular oxygen. It is a strong oxidizing agent and has been used in water conditioning as a disinfectant. It can be also produced by some types of ultraviolet lamps and during lightning storms.
Ozone Generator	A device that generates ozone by passing a voltage through a chamber that contains oxygen. It is often used as a disinfection system.

Paleohydrology	Study of hydrologic processes and events, using geological, botanical, and cultural evidence, that occurred before the beginning of the systematic collection of hydrologic data and observations.
Palustrine Wetlands	Freshwater wetlands including open water bodies of less than 20 acres in which water is less than 2 meters deep; includes marshes, wet meadows, fens, playas, potholes, pocosins, bogs, swamps, and shallow ponds; most wetlands are in the Palustrine system.
Parameter	A variable, measurable property whose value is a determinant of the characteristics of a system such as water. Temperature, pressure, and density are examples of parameters.
Part Per Million (ppm)	Unit of concentration equal to one milligram per kilogram or one milligram per liter.
Partial Pressure	That pressure of a gas in a liquid, which is in equilibrium with the solution. In a mixture of gases, the partial pressure of any one gas is the total pressure times the fraction of the gas in the mixture (by volume or number of molecules).
Particle Size	The diameter, in millimeters, of suspended sediment or bed material.
Particulate	A term used to describe visible sediment particles, used as both singular and plural.
Particulate Loading	The mass of particulates per unit volume of water.
Parts Per Billion (ppb)	A basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of a dissolved or suspended constituent, per billion parts by weight of water or other solvent. One part per billion is equal to one microgram per liter, the preferred unit.
Parts Per Million (ppm)	A common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit. 17.l ppm equals one grain per US gallon. One ppm equals one pound per million pounds of water.
Pasteurization	The elimination of microorganisms by heat applies for a certain period of time.
Pathogen	A disease-producing agent; usually applied to a living organism. Generally, any viruses, bacteria, or fungi that cause disease.
Pathogens	Disease-producing microorganisms.
Peak Flow	The maximum instantaneous discharge of a stream or river at a given location. It usually occurs at or near the time of maximum stage.
Peak Stage	Maximum height of a water surface above an established datum plane. Same as peak gage height.
Peat	A highly organic soil, composed of partially decomposed vegetable matter.
Per Capita Use	The average amount of water used per person during a standard time period, generally per day.
Percent Saturation	The amount of a substance that is dissolved in a solution compared to the amount that could be dissolved in it.
Percentile	The value below which a given percentage of observations in a group of observations fall. For example, the 20th percentile is the value below which 20 percent of the observations may be found.
Perched Ground Water	Unconfined ground water separated from an underlying main body of ground water by an unsaturated zone.
Percolating Water	Water that passes through rocks or soil under the force of gravity.
Percolation	(1) The movement of water through the openings in rock or soil. (2) the entrance of a portion of the streamflow into the channel materials to contribute to groundwater replenishment.
Perennial Stream	A stream that normally has water in its channel at all times.
Periodic Chart	Arrangement of elements in order of increasing atomic numbers, created by a scientist called Mendelejef.
Periphyton	Micro-organisms that coat rocks, plants, and other surfaces on lake bottoms.
Permafrost	Any frozen soil, subsoil, surficial deposit, or bedrock in arctic or subarctic regions where below-freezing temperatures have existed continuously from two to tens of thousands of years.
Permeability	The ability of a material to allow the passage of a liquid, such as water through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas unpermeable material, such as clay, don't allow water to flow freely.
Persistence	Refers to the length of time a compound stays in the environment, once introduced.
Pesticide	Any substance used to kill plant or animal pests; major categories of pesticides include herbicides and insecticides.
pH (potential of Hydrogen)	An expression of the acidity of a solution; the negative logarithm of the hydrogen ion concentration (pH 1 very acidic; pH 14, very basic; pH 7, neutral). e.g., pH 5 is 10 times the acidity of 6 and 100 times the acidity of 7. pH is a measure of intensity and not capacity. It is the logarithm of the reciprocal of the hydrogen ion concentration of a solution. The neutral point of 7 indicates the presence of equal concentrations of free hydrogen and free hydroxide ions.
Pharmaceutical Grade Water	The definition of six grades of water by the U.S. Pharmacopoeia is as follows: 1.) Purified water 2.) Water for injection 3.) Bacteriostatic water for injection 4.) Sterile water for inhalation 5.) Sterile water for injection 6.) Sterile water for irrigation.
Phase	A state of matter. This can be solid, liquid or gaseous.
Phenolphthalein	An acid-base indicator which produces no color in an acid solution but turns pink or red in an alkaline solution.
Phenols	A class of organic compounds containing phenol (C6H5OH) and its derivatives. Used to make resins, weed killers, and as a solvent, disinfectant, and chemical intermediate. Some phenols occur naturally in the environment.
Phosphorus	A nutrient essential for growth that can play a key role in stimulating aquatic growth in lakes and streams.
Photosynthesis	A process in which organisms, with the aid of chlorophyll, convert carbon dioxide and inorganic substances into oxygen and additional plant material, using sunlight for energy. All green plants grow by this process.
Phthalates	A class of organic compounds containing phthalic acid esters [C6H4(COOR)2] and derivatives. Used as plasticizers in plastics. Also used in many other products (such as detergents, cosmetics) and industrial processes (such as defoaming agents in paper and paperboard manufacture, and dielectrics in capacitors).
Physical Adsorption (Van der Waals Adsorption)	Binding of adsorbate to the surface of a solid by forces whose energy levels approximate those of condensation.
Physical and Chemical Treatment	Processes generally used in wastewater treatment facilities. Physical processes are for instance filtration. Chemical treatment can be coagulation, chlorination, or ozone treatment.
Physical Stability	The quality which an ion exchange resin must possess to resist changes that might be caused by attrition, high temperatures, and other physical conditions.
Physical Weathering	Breaking down of rock into bits and pieces by exposure to temperature and changes and the physical action of moving ice and water, growing roots, and human activities such as farming and construction.
Physiographic Province	A region in which the landforms are distinctive and differ significantly from those of adjacent regions.
Physiography	A description of the surface features of the Earth, with an emphasis on the origin of landforms.
Phytoplankton	Small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water.
Picocurie (pCi)	One trillionth (10-12) of the amount of radioactivity represented by a curie (Ci). A curie is the amount of radioactivity that yields 3.7 x 1010radioactive disintegrations per second (dps). A picocurie yields 2.22 disintegrations per minute (dpm) or 0.037 dps.
Pilot Tests	The testing of a cleanup technology under actual site conditions in a laboratory in order to identify potential problems before implementation.
Pioneer Plant	Herbaceous annual and perennial seedling plants that colonize bare areas as a first stage in secondary succession.
Piping	Erosion by percolating water in a layer of subsoil, resulting in caving and in the formation of narrow conduits, tunnels, or pipes through which soluble or granular soil material is removed.
Placer	A surficial mineral deposit formed by mechanical concentration of mineral particles from weathered debris.
Plankton	Small, usually microscopic, plants (phytoplankton) and animals (zooplankton) in aquatic systems.
Playa	A dry, flat area at the lowest part of an undrained desert basin in which water accumulates and is quickly evaporated; underlain by stratified clay, silt, or sand and commonly by soluble salts; term used in Southwestern United States.
Playa Lake	A shallow, temporary lake in an arid or semiarid region, covering or occupying a playa in the wet season but drying up in summer; temporary lake that upon evaporation leaves or forms a playa.
Pocosin	A local term along the Atlantic coastal plain, from Virginia south, for a shrub-scrub wetland located on a relatively flat terrain, commonly between streams.
POE	Treatment-Point-Of-Entry treatment. Total water treatment at the inlet to an entire building or facility.
Point	Source contaminant- Any substance that degrades water quality and originates from discrete locations such as discharge pipes, drainage ditches, wells, concentrated livestock operations, or floating craft.
Point Of Entry (POE)	A water treatment device which installs at the main inlet to a building and acts as centralized treatment.
Point Of Use (POU)	A water treatment system designed to connect at the actual point-of-use for water; countertop or undersink treatment systems.
Point Source	A discharge, often containing pollutants, from the end of a pipe or other clearly identifiable conveyance, such as ditches, channels, tunnels, conduits, wells, containers, rolling stock, concentrated animal feeding operations, landfill leachate collection systems, vessels, or other floating craft.
Point-Source Pollution	Water pollution coming from a single point, such as a sewage-outflow pipe.
Polar Substance	A substance that carries a positive or negative charge, for instance water.
Pollutant	Any substance that causes an impairment (reduction) of water quality to a degree that has an adverse effect on any beneficial use of the water.
Polychlorinated Biphenyls (PCBs)	A group of synthetic, toxic industrial chemical compounds also known as PCBs once used in making paint and electrical transformers, which are chemically inert and not biodegradable. PCBs were frequently found in industrial wastes, and subsequently found their way into surface and groundwaters.
Polycyclic Aromatic Hydrocarbon (PAH)	A class of organic compounds with a fused-ring aromatic structure. PAHs result from incomplete combustion of organic carbon (including wood), municipal solid waste, and fossil fuels, as well as from natural or anthropogenic introduction of uncombusted coal and oil. PAHs include benzo(a)pyrene, fluoranthene, and pyrene.
Polyphosphate	A sequestering agent used to tie up hardness and iron in solution. As a coating agent, it forms a thin passivating film on metal surfaces to control corrosion.
Pool	A small part of a stream reach with little velocity, commonly with water deeper than surrounding areas.
POP's	Persistent Organic Pollutants, complex compounds that are very persistent and difficultly biologically degradable.
Population	A collection of individuals of one species or mixed species making up the residents of a prescribed area.
Pore	An opening in a membrane or medium that allows water to pass through.
Pores	The complex network of channels in the interior of a particle of a sorbent.
Porosity	A measure of the water-bearing capacity of subsurface rock. With respect to water movement, it is not just the total magnitude of porosity that is important, but the size of the voids and the extent to which they are interconnected, as the pores in a formation may be open, or interconnected, or closed and isolated.
Portable Exchange	Water softeners, deionizers, and filters which are designed for removal from its point of application for transport to a central station or plant for regeneration or servicing.
Positive Charge	The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.
Positive Displacement Water Meters	A positive displacement meter is a type of flow meter that requires fluid to mechanically displace components in the meter in order for flow measurement. On an oval gear type meter, fluid forces meshed gears to rotate; each rotation corresponds to a fixed volume of fluid. Counting the revolutions totalizes volume, and the rate is proportional to flow. On a nutating disc type meter, a disc mounted on a sphere is “wobbled” about an axis by the fluid flow and each rotation represents a finite amount of fluid transferred. A nutating disc flow meter has a round disc mounted on a spindle in a cylindrical chamber. By tracking the movements of the spindle, the flow meter determines the number of times the chamber traps and empties fluid. This information is used to determine the flow rate.
Postemergence Herbicide	Herbicide applied to foliage after the crop has sprouted to kill or significantly retard the growth of weeds.
Potable Water	Potable water is also known as drinking water and comes from surface water and groundwater sources. Uses can include drinking, bathing, irrigation, and fire protection. This water is treated to levels that meet state and federal standards for consumption. The word, “potable” comes from the Latin potare, meaning "to drink." The Romans came up with the word and built some of the world's first aqueducts, above-ground channels that brought potable water from the mountains to the cities.
Potential evapotranspiration	The amount of moisture which, if available, would be removed from a given land area by evapotranspiration; expressed in units of water depth.
Potentiation	The ability of one chemical to increase the effect of another chemical.
Potentiometric Surface	A surface representing the hydraulic head of ground water; represented by the water-table altitude in an unconfined aquifer or by the altitude to which water will rise in a properly constructed well in a confined aquifer.
Potentiometric Surface/Piezometric Surface	The imaginary line where a given reservoir of fluid will equalize out to if allowed to flow; a potentiometric surface is based on hydraulic principles.
POU Treatment	Point-Of-Use treatment. Water treatment at a limited number of outlets in a building, for less than the whole building.
Powdered Activated Carbon	Activated carbon in particle sizes predominantly smaller than 80 mesh.
PPB	The abbreviation for parts per billion.
PPM	The abbreviation for parts per million.
Prairie Pothole	A shallow depression, generally containing wetlands, occurring in an outwash plain, a recessional moraine, or a till plain; usually the result of melted blocks of covered glacial ice; occur most commonly in the North-Central United States and in States west of the Great Lakes from Wisconsin to eastern Montana.
Pre	Treatment-Processes used to reduce or eliminate wastewater pollutants from before they are discharged.
Pre Chlorination	The application of chlorine to a water prior to other water treatment processes.
Precipitate	To cause a dissolved substance to form a solid particle that can be removed by settling or filtering.
Precipitation	Any or all forms of water particles that fall from the atmosphere, such as rain, snow, hail, and sleet. The act or process of producing a solid phase within a liquid medium.
Precipitation Process	The altering of dissolved compounds to insoluble or badly soluble compounds, in order to be able to remove the compounds by means of filtration.
Preemergence Herbicide	Herbicide applied to bare ground after planting the crop but prior to the crop sprouting above ground to kill or significantly retard the growth of weed seedlings.
Preferential Adsorption	Adsorption in which a certain component or certain components are adsorbed to a much greater extent than others.
Pressure Drop	A decrease in water pressure during its flow due to internal friction between molecules of water, and external friction due to irregularities or roughness in surfaces past which the water flows.
Pressure Sewers	A system of pipes in which water, wastewater, or other liquid is pumped to a higher elevation.
Primary Wastewater Treatment	The first process usually associated with municipal wastewater treatment to remove the large inorganic solids and settle out sand and grit.
Prior Appropriation Doctrine	The system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid West as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of First in Time, First in Right. The first person to take a quantity of water and put it to beneficial use has a higher priority of right than a subsequent user. The rights can be lost through nonuse; they can also be sold or transferred apart from the land. Contrasts with riparian water rights.
Pristine	The earliest condition of the quality of a water body; unaffected by human activities.
Process Water	Water which can not be classified as drinking water and which is used in connection with technical plants and processes in production companies, heat and power plants, and institutions.
Protons	Positively charged building blocks of an atom that are centered in the nucleus.
Protozoa	A group of motile, microscopic organisms (usually single-celled and aerobic) that sometimes cluster into colonies and generally consume bacteria as an energy source.
Public	Supply withdrawals- Water withdrawn by public and private water suppliers for use within a general community. Water is used for a variety of purposes such as domestic, commercial, industrial, and public water use.
Public Supply	Water withdrawn by public governments and agencies, such as a county water department, and by private companies that is then delivered to users. Public suppliers provide water for domestic, commercial, thermoelectric power, industrial, and public water users. Most people's household water is delivered by a public water supplier. The systems have at least 15 service connections (such as households, businesses, or schools) or regularly serve at least 25 individuals daily for at least 60 days out of the year.
Public Water System	A system that provides piped water for human consumption to at least 15 service connections or regularly serves 25 individuals.
Public Water Use	Water supplied from a public-water supply and used for such purposes as firefighting, street washing, and municipal parks and swimming pools.
Pumicite	A natural, glassy aluminum silicate mineral from volcanic ash which is used as a water treatment filtration media.
Purification	The removal of undesirable matter from water or wastewater. It is the disinfection of water by the killing of microbial contaminants, such as coliform bacteria. A strict definition means the removal from water of all contaminants.
Putrefaction	Biological decomposition of organic matter, with the production of foul-smelling and -tasting products, associated with anaerobic (no oxygen present) conditions.
Pyrogen	Substances which produce fever when introduced into humans. Being chemically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria.
Pyrolox	A super oxidation media serving as a catalyst in the removal of iron, hydrogen sulfide and manganese. It works best at or above a pH of 6.5 and requires no regeneration. Adequate backwashing is necessary to provide at least 20 per cent bed expansion of this 120 lb. per cubic foot media.

R.O.	The abbreviation for reverse osmosis.
Radioactive	Having the property of releasing radiation.
Radium	Naturally occurring radioactive elements such as radium 226 and radium 228 created in the decay of the uranium and thorium series. It can be removed from water by cation exchange softening.
Radon	A short lived radioactive gas produced from decaying uranium that is soluble in water. Can be effectively removed by activated carbon filtration or serration. Radon is considered carcinogenic when inhaled by humans.
Rain Shadow	A dry region on the lee side of a topographic obstacle, usually a mountain range, where rainfall is noticeably less than on the windward side.
Rating Curve	A drawn curve showing the relation between gage height and discharge of a stream at a given gaging station.
Raw Sewage	Untreated wastewater and its contents.
Raw Water	Water in its natural state, before any treatment, especially as it enters the first treatment process of a water treatment plant.
Reach	A continuous part of a stream between two specified points.
Reactivation (Revivification)	Oxidation processes for restoring the adsorptive properties of a spent sorbent such as activated carbon.
Reaeration	The introduction of air through forced air diffusers into the lower layers of the reservoir. As the air bubbles form and rise through the water, oxygen from the air dissolves into the water and replenishes the dissolved oxygen.
Real	Time data- Data collected by automated instrumentation and telemetered and analyzed quickly enough to influence a decision that affects the monitored system.
Recarbonization	Process in which carbon dioxide is bubbled into treatment water in order to lower the pH.
Receiving Waters	A river, lake, ocean, stream or other watercourse into which wastewater or treated effluent is discharged.
Recessional Moraine	An endmorainebuilt during a temporary but significant pause in the final retreat of a glacier.
Recharge (ground water)	The process involved in the absorption and addition of water to the zone of saturation; also, the amount of water added.
Recharge Area	An area in which water reaches the zone of saturation by surface infiltration.
Recharge Area (ground water)	The area in which water enters an aquifer . In a recharge zone surface water or precipitation percolate through relatively porous, unconsolidated, or fractured materials, such as sand, moraine deposits, or cracked basalt, that lie over a water bearing, or aquifer, formation.
Recirculation	Recycling water after it is used. Often it has to pass a wastewater purification system before it can be reused.
Reclaimed Wastewater	Wastewater-treatment plant effluent that has been diverted for beneficial uses such as irrigation, industry, or thermoelectric cooling instead of being released to a natural waterway or aquifer.
Recurrence Interval	The average interval of time within which the magnitude of a given event, such as a storm or flood, will be equaled or exceeded once.
Recycled Water	Water that is used more than one time before it passes back into the natural hydrologic system.
Redox	Redox reactions involve electron transfers; if one species gains electrons, another species (or more than one species) must lose electrons.
Reduction	A chemical reaction in which ions gain electrons to reduce their positive valence.
Regenerant	The solution used to restore the activity of an ion exchanger. Acids are employed to restore a cation exchanger to its sodium form. The anion exchanger may be rejuvenated by treatment with an alkaline solution. Potassium permanganate is used to regenerate a manganese greensand iron and manganese iron and manganese removal filter.
Regeneration	Regeneration is the process of restoring an ion exchange medium to a usable state after exhaustion.
Regolith	The layer or mantle of fragmented and unconsolidated rock material, residual or transported, that nearly everywhere forms the surface of the land and overlies or covers the bedrock.
Regulation (of a stream)	Artificial manipulation of the flow of a stream.
Rejection	In crossflow membrane filtration and deionization, it is the ability of the membrane to reject the passage of dissolved solids and other contaminants into the product water.
Relative Abundance	The number of organisms of a particular kind present in a sample relative to the total number of organisms in the sample.
Reserve Capacity	Extra treatment capacity built into wastewater treatment plants and sewers to be able to catch up with future flow increases due to population growth.
Reservoir	A pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water.
Residential Water Use	See Domestic withdrawals.
Residual	The amount of a specific material remaining in the water following a water treatment process. It may refer to material remaining as the result of incomplete removal such as hardness leakage, or to a substance meant to remain in the treated water such as residual chlorine.
Residue	The dry solids remaining after the evaporation of a sample of water or sludge.
Resin	Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners. Technical name- sulfonated co-polymer of styrene and divinyl benzene.
Resolution	The breaking of an emulsion into its individual components.
Retentivity	The ability of an adsorbent to resist desorption of an adsorbate.
Return Flow	(1) That part of a diverted flow that is not consumptively used and returned to its original source or another body of water. (2) (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream.
Return Flow (irrigation)	Irrigation water that is applied to an area and which is not consumed in evaporation or transpiration and returns to a surface stream or aquifer.
Reverse Deionization	The use of an anion exchange unit ahead of a cation exchange unit- in that order- in a deionization system.
Reverse Osmosis	(1) (Desalination) The process of removing salts from water using a membrane. With reverse osmosis, the product water passes through a fine membrane that the salts are unable to pass through, while the salt waste (brine) is removed and disposed. This process differs from electrodialysis, where the salts are extracted from the feedwater by using a membrane with an electrical current to separate the ions. The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end product of freshwater. (2) (Water Quality) An advanced method of water or wastewater treatment that relies on a semi-permeable membrane to separate waters from pollutants. An external force is used to reverse the normal osmotic process resulting in the solvent moving from a solution of higher concentration to one of lower concentration.
Reverse Osmosis process	The Reversed Osmosis (RO) process uses a semi-permeable membrane to separate and remove dissolved solids, organics, pyrogens, submicron colloidal matter, viruses, and bacteria from water. The process is called 'reverse' osmosis since it requires pressure to force pure water across a membrane, leaving the impurities behind.
Riffle	A shallow part of the stream where water flows swiftly over completely or partially submerged obstructions to produce surface agitation.
Riparian	Pertaining to or situated on the bank of a natural body of flowing water.
Riparian Rights	A concept of water law under which authorization to use water in a stream is based on ownership of the land adjacent to the stream.
Riparian Water Rights	The rights of an owner whose land abuts water. They differ from state to state and often depend on whether the water is a river, lake, or ocean. The doctrine of riparian rights is an old one, having its origins in English common law. Specifically, persons who own land adjacent to a stream have the right to make reasonable use of the stream. Riparian users of a stream share the streamflow among themselves, and the concept of priority of use (Prior Appropriation Doctrine) is not applicable. Riparian rights cannot be sold or transferred for use on nonriparian land.
Riparian Zone	Pertaining to or located on the bank of a body of water, especially a stream.
River	A natural stream of water of considerable volume, larger than a brook or creek.
Riverine Wetlands	Wetlands within river and stream channels; ocean-derived salinity is less than 0.5 part per thousand.
Rock	Any naturally formed, consolidated or unconsolidated material (but not soil) consisting of two or more minerals.
Runoff	That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or groundwater runoff.
Rural Withdrawals	Water used in suburban or farm areas for domestic and livestock needs. The water generally is self-supplied and includes domestic use, drinking water for livestock, and other uses such as dairy sanitation, evaporation from stock-watering ponds, and cleaning and waste disposal.
Rust (ferric oxide)	A reddish product of corrosion sometimes found in water. Rust is formed as a result of electrochemical interaction between iron and oxygen in the presence of moisture.

Sacrificial Anode	An anode constructed of magnesium or other suitable material and placed in a water heater tank to accept the electrolytic activity and to protect the tank from corrosion.
Safe Water	Water that does not contain harmful bacteria, toxic materials, or chemicals, and is considered safe for drinking.
Safe Yield	The annual amount of water that can be taken from a source of supply over a period of years without depleting that source beyond its ability to be naturally refilled.
Salina	An area where deposits of crystalline salt are formed, such as a salt flat; a body of saline water, such as a saline playa or salt marsh.
Saline Water	Water that is considered unsuitable for human consumption or for irrigation because of its high content of dissolved solids; generally expressed asmilligrams per liter(mg/L) of dissolved solids; seawater is generally considered to contain more than 35,000 mg/L of dissolved solids.
Salinity	The presence of soluble minerals in water.
Salt	The common name for the specific chemical compound sodium chloride (NaCl), used in the regeneration of ion exchange water softeners. In chemistry, the term is applied to a class of chemical compounds which can be formed by the neutralization of an acid with a base.
Sand	As a soil separate, individual rock or mineral fragments from 0.05 millimeter to 2.0 millimeters in diameter. Most sand grains consist of quartz. As a soil textural class, a soil that is 85 percent or more sand and not more than 10 percent clay.
Sand Filter	A treatment device or structure for removing solid or colloidal material of a type that cannot be removed by sedimentation. Such filters can be gravity rapid-rate or enclosed pressure type.
Sand Filtration	Sand filtration is a frequently used and very robust method to remove suspended solids from water. The filtration medium consists of a multiple layer of sand with a variety in size and specific gravity. Sand filters can be supplied in different sizes and materials both hand operated and fully automatically.
Saturated Solution	A solution containing the maximum amount of the dissolved substance that such a solution can hold at this temperature.
Saturated Zone	A zone in which all the pores and rock fractures are filled with water, underlies the unsaturated zone. The top of the saturated zone is called the water table.
Saturation	The condition of a liquid when it has taken into solution the maximum possible quantity of a given substance.
Scale	The precipitate that forms on surfaces in contact with water as the result of a physical or chemical change.
Scavenger	A polymer matrix or ion exchanger used to remove organics from feedwater prior to a deionization process.
Screening	Use of screens to remove coarse floating and suspended solids from sewage.
Sea level	Long-term average position of the sea surface. Sea level varies from place to place and with the time period for which the average is calculated. For the conterminous United States, sea level is most commonly referenced to theNational Geodetic Vertical Datum of 1929.
Sea water	See Saline water.
Secondary Maximum Contaminant Level (SMCL)	The maximum level of a contaminant or undesirable constituent in public water systems that, in the judgment of the U.S. Environmental Protection Agency (USEPA), is required to protect the public welfare. SMCLs are secondary (nonenforceable) drinking water regulations established by the USEPA for contaminants that may adversely affect the odor or appearance of such water.
Secondary Treatment	The removal or reduction of contaminants and BOD of effluent from primary wastewater treatment.
Secondary Wastewater Treatment	Treatment (following primary wastewater treatment) involving the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent from primary treatment systems and which generally removes 80 to 95 percent of the Biochemical Oxygen Demand (BOD) and suspended matter. Secondary wastewater treatment may be accomplished by biological or chemical-physical methods. Activated sludge and trickling filters are two of the most common means of secondary treatment. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This treatment removes floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.
Sediment	Particles, derived from rocks or biological materials, that have been transported by a fluid or other natural process, suspended or settled in water.
Sediment Guideline	Threshold concentration above which there is a high probability of adverse effects on aquatic life from sediment contamination, determined using modified U.S. Environmental Protection AgencyUSEPA (1996)procedures.
Sedimentary Rock	Rock formed of sediment, and specifically: (1) sandstone and shale, formed of fragments of other rock transported from their sources and deposited in water; and (2) rocks formed by or from secretions of organisms, such as most limestone. Many sedimentary rocks show distinct layering, which is the result of different types of sediment being deposited in succession.
Sedimentation	The process of allowing particles in suspension in water to settle out of the suspension under the effect of gravity.
Sedimentation Tanks	Wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal.
Sediments	Soil, sand, and minerals washed from land into water, usually after rain.
Seep	A small area where water percolates (seepercolation) slowly to the land surface.
Seepage	(1) The slow movement of water through small cracks, pores, Interstices, etc., of a material into or out of a body of surface or subsurface water. (2) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, or other body of water, or from a field.
Seiche	A sudden oscillation of the water in a moderate-size body of water, caused by wind.
Selective Herbicide	A compound that kills or significantly retards growth of an unwanted plant species without significantly damaging desired plant species.
Selective Ion Exchange	The use of a selective ion exchange medium with the property of removing specific ions from a solution.
Self-Supplied Water	Water withdrawn from a surface- or groundwater source by a user rather than being obtained from a public supply. An example would be homeowners getting their water from their own well.
Semi Confined Aquifer	An aquifer partially confined by soil layers of low permeability through which recharge and discharge can still occur.
Semipermeable	A medium that allows water to pass through, but rejects dissolved solids, so that it can be used to separate solids from water.
Semipermeable Membrane Device (SPMD)	A long strip of low-density, polyethylene tubing filled with a thin film of purified lipid such as triolein that simulates the exposure to and passive uptake of highly lipid-soluble organic compounds by biological membranes.
Semivolatile Organic Compound (SVOC)	Operationally defined as a group of synthetic organic compounds that are solvent-extractable and can be determined by gas chromatography/mass spectrometry. SVOCs include phenols, phthalates, and Polycyclic aromatic hydrocarbons (PAHs).
Separate Sewer	A sewer system that carries only sanitary sewage; no stormwater runoff. When a sewer is constructed this way, wastewater treatment plants can be sized to treat sanitary wastes only and all of the water entering the plant receives complete treatment at all times.
Separation	The isolation of the various compounds in a mixture.
Septic Tank	A septic tank is an underground tank where faeces, urine, and other waste matter is made harmless using bacteria.
Sequester	A chemical reaction in which certain ions are bound into a stable, water soluble compound, thus preventing undesirable action by the ions. For example, polyphosphates can sequester hardness and prevent reactions with soap.
Service Run	That portion of the operating cycle of a water conditioning unit during which treated water is being delivered, as opposed to the period when the unit is being backwashed, recharged or regenerated.
Settleable Solids	Those suspended solids in wastewater that will settle over a certain period of time and are removed in that way.
Settling	The process of sinking of a substance sinking in water. This occurs when the substance does not dissolve in water and its density is larger than that of water.
Settling Pond (water quality)	An open lagoon into which wastewater contaminated with solid pollutants is placed and allowed to stand. The solid pollutants suspended in the water sink to the bottom of the lagoon and the liquid is allowed to overflow out of the enclosure.
Sewage	Waste fluid in a sewer system.
Sewage Contamination	The introduction of untreated sewage into a water body.
Sewage Cludge	Sludge produced in a public sewer.
Sewage Treatment Plant	A facility designed to receive the wastewater from domestic sources and to remove materials that damage water quality and threaten public health and safety when discharged into receiving streams or bodies of water. Most facilities employ a combination of mechanical removal steps and bacterial decomposition to achieve the desired results. Chlorine is often added to discharges from the plants to reduce the danger of spreading disease by the release of pathogenic bacteria.
Sewer	A system of underground pipes that collect and deliver wastewater to treatment facilities or streams.
Sewerage	The entire system of sewage collection, treatment, and disposal.
Shale	A fine-grained sedimentary rock formed by the consolidation of clay, silt, or mud.
Shallows	A term applied to a shallow place or area in a body of water; ashoal.
Shoal	A relatively shallow place in a stream, lake, or sea.
Short	Wave trough (meteorlogical)- A wave of low atmospheric pressure in the form of a trough that has a wave length of 600 to 1,500 miles and moves progressively through the lowertroposphere in the same direction as that of the prevailing current of air motion.
Shrubland	Land covered predominantly with shrubs.
Sideslope Gradient	The representative change in elevation in a given horizontal distance (usually about 300 yards) perpendicular to a stream; the valley slope along a line perpendicular to the stream (near a water-quality or biological sampling point).
Siliceous Gel Zeolite	A synthetic, inorganic exchanger produced by the aqueous reaction of alkali with aluminum salts.
Siliciclastic Rocks	Rocks such as shale and sandstone that are formed by the compaction and cementation of quartz-rich mineral grains.
Silt	Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water (also known as a suspended load) and soil in a body of water such as a river. Individual mineral particles range in diameter from the upper limit of clay (0.002 millimeter) to the lower limit of very fine sand (0.05 millimeter).
Siltation	The deposition or accumulation of silt (or small-grained material) in a body of water.
Siltstone	Aninduratedsilt having the texture and composition of shale but lacking its fine lamination.
Silviculture	The cultivation of forest trees.
Sinkhole	A depression in the Earth's surface caused by dissolving of underlying limestone, salt, or gypsum. Drainage is provided through underground channels that may be enlarged by the collapse of a cavern roof.
Sinuosity	The ratio of the channel length between two points on a channel to the straight-line distance between the same two points; a measure of meandering.
Skewness	Numerical measure of the lack of symmetry of an asymmetrical frequency distribution.
Slightly Saline Water	From 1,000 ppm to 3,000 ppm dissolved solids
Slough	A small marshy tract lying in aswaleor other local shallow, undrained depression; a sluggish creek or channel in a wetland.
Sludge	A semi-solid residue, containing microorganisms and their products, from any water treatment process.
Soda Ash	The common name for sodium carbonate, a chemical compound used as an alkaline builder in some soap and detergent formulations, to neutralize acid water, and in the lime- soda ash water treatment process.
Sodium Hydrosulfite	A strong reducing agent used as the main ingredient of several resin cleaners used to clean iron fouled in ion exchange resin beds.
Soft Water	Any water that does not contain large concentrations of the dissolved minerals calcium or magnesium.
Softened Water	Any water that is treated to reduce hardness minerals to 1.0 GPG (17.1 mg/L) or less, expressed as calcium carbonate.
Softening	The removal of calcium and magnesium from water to reduce hardness.
Soil	The layer of material at the land surface that supports plant growth.
Soil Horizon	A layer of soil that is distinguishable from adjacent layers by characteristic physical and chemical properties.
Soil Moisture	Water occurring in the pore spaces between the soil particles in the unsaturated zone from which water is discharged by the transpiration of plants or by evaporation from the soil.
Sole	Source aquifer- As defined by the U.S. Environmental Protection Agency, anaquiferthat supplies 50 percent or more of the drinking water of an area.
Solid	Phase extraction- A procedure to isolate specific organic compounds onto a bonded silica extraction column.
Solidification	Removal of wastewater from a waste or changing it chemically to make it less permeable and susceptible to transport by water.
Solubility	The amount of mass of a compound that will dissolve in a unit volume of water.
Solute	A substance that is dissolved in another substance, thus forming a solution.
Solution	A mixture of a solvent and a solute. In some solutions, such as sugar water, the substances mix so thoroughly that the solute cannot be seen. But in other solutions, such as water mixed with dye, the solution is visibly changed.
Solvent	A substance that dissolves other substances, thus forming a solution. Water dissolves more substances than any other, and is known as the "universal solvent".
Sorb	To take up and hold either by absorption or adsorption.
Sorption	General term for the interaction (binding or association) of a solute ion or molecule with a solid.
Source Rocks	The rocks from which fragments and other detached pieces have been derived to form a different rock.
Sparger	A device that introduces compressed air into a liquid.
Sparging	Injection of air below the water table to strip dissolved volatile organic compounds and to facilitate aerobic biodegradation of organic compounds.
Species	Populations of organisms that may interbreed and produce fertile offspring having similar structure, habits, and functions.
Species (taxa) Richness	The number of species (taxa) present in a defined area or sampling unit.
Species Diversity	An ecological concept that incorporates both the number of species in a particular sampling area and the evenness with which individuals are distributed among the various species.
Specific Capacity	The yield of a well per unit of drawdown.
Specific Conductance	A measure of the ability of water to conduct an electrical current as measured using a 1-cm cell and expressed in units of electrical conductance, i.e., Siemens per centimeter at 25 degrees Celsius. Specific conductance can be used for approximating the total dissolved solids content of water by testing its capacity to carry an electrical current. In water quality, specific conductance is used in groundwater monitoring as an indication of the presence of ions of chemical substances that may have been released by a leaking landfill or other waste storage or disposal facility.
Specific Yield	The ratio of the volume of water that will drain under the influence of gravity to the volume of saturated rock.
Spit	A small point or low tongue or narrow embankment of land having one end attached to the mainland and the other terminating in open water.
Split Sample	A sample prepared by dividing it into two or more equal volumes, so that each volume is considered a separate sample but representative of the entire sample.
Spoil	Overburden or other waste material removed in mining, quarrying, dredging, or excavating.
Sprain	An archaic term (1600's) referring to a spring or branch of a river. Spelling was sprayne.
Spray Irrigation	A common irrigation method where water is shot from high-pressure sprayers onto crops. Because water is shot high into the air onto crops, some water is lost to evaporation.
Spring	A water body formed when the side of a hill, a valley bottom or other excavation intersects a flowing body of groundwater at or below the local water table, below which the subsurface material is saturated with water.
Stage	Height of the water surface above an establisheddatum plane, such as in a river above a predetermined point that may (or may not) be at the channel floor.
Standard Deviation	Statistical measure of the dispersion or scatter of a series of values. It is the square root of the variance, which is calculated as the sum of the squares of the deviations from the arithmetic mean, divided by the number of values in the series minus 1 .
State Climate Division	Geographic area in a State based primarily on crop-reporting districts. States can have 2 to 10 climate divisions.
Statistics	A branch of mathematics dealing with the collection, analysis, interpretation, and presentation of masses of numerical data.
Stoke's Law	A method to calculate the rate of fall of particles through a fluid, based on density, viscosity and particle size.
Storm Sewer	A sewer that carries only surface runoff, street wash, and snow melt from the land. In a separate sewer system, storm sewers are completely separate from those that carry domestic and commercial wastewater (sanitary sewers).
Storm Surge	An abnormal and sudden rise of the sea along a shore as a result of the winds of a storm.
Stream	A general term for a body of flowing water; natural water course containing water at least part of the year. In hydrology, it is generally applied to the water flowing in a natural channel as distinct from a canal.
Stream Mile	A distance of 1 mile along a line connecting the midpoints of the channel of a stream.
Stream Order	A ranking of the relative sizes of streams within a watershed based on the nature of their tributaries. The smallest unbranched tributary is called first order, the stream receiving the tributary is called second order, and so on.
Stream Reach	A continuous part of a stream between two specified points.
Streamflow	The water discharge that occurs in a natural channel. A more general term than runoff, streamflow may be applied to discharge whether or not it is affected by diversion or regulation.
Streamline	A line on a map that is parallel to the direction of fluid flow and shows flow patterns.
Sublimation	The transitions of water directly from the solid state to the gaseous state, without passing through the liquid state.
Submersed Plant	A plant that lies entirely beneath the water surface, except for flowering parts in some species.
Subsidence	A dropping of the land surface as a result of groundwater being pumped. Cracks and fissures can appear in the land. Subsidence is virtually an irreversible process.
Substrate	The surface beneath a wetland, lake, or stream in which organisms grow or to which organisms are attached.
Substrate Size	The diameter of streambed particles such as clay, silt, sand, gravel, cobble and boulders.
Subsurface Drain	A shallow drain installed in an irrigated field to intercept the rising ground-water level and maintain the water table at an acceptable depth below the land surface.
Subtidal	Continuously submerged; an area affected by ocean tides.
Subtropical Anticyclone	A semipermanent anticyclone located, on the average, over oceans near
Sulfur	A yellowish solid chemical element. The term is also used as a slang expression to refer to water containing hydrogen sulfide gas (H2 S).
Supernatum	The top level of a fluid at rest; important in many applications of water and wastewater treatment. In particular, it is of concern and often measured in settling tanks and skimmers.
Surface Runoff	Runoff that travels over the land surface to the nearest stream channel.
Surface Tension	The elastic like force existing in the surface of a body, especially a liquid, tending to minimize the area of the surface, caused by asymmetries in the intermolecular forces between surface molecules.
Surface Water	Water that is on the Earth's surface, such as in a stream, river, lake, or reservoir.
Survey	Sampling of a representative number of sites during a given hydrologic condition.
Suspended Sediment	Very fine soil particles that remain in suspension in water for a considerable period of time without contact with the bottom. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension.
Suspended solids	Solids that are not in true solution and that can be removed by filtration. Such suspended solids usually contribute directly to turbidity. Defined in waste management, these are small particles of solid pollutants that resist separation by conventional methods.
Suspended-Sediment Concentration	The ratio of the mass of dry sediment in a water-sediment mixture to the mass of the water-sediment mixture. Typically expressed in milligrams of dry sediment per liter of water-sediment mixture.
Suspended-Sediment Discharge	The quantity of suspended sediment passing a point in a stream over a specified period of time. When expressed in tons per day, it is computed by multiplying water discharge (in cubic feet per second) by the suspended-sediment concentration (in milligrams per liter) and by the factor 0.0027.
Swale	A slight depression, sometimes filled with water, in the midst of generally level land.
Swamp	An area intermittently or permanently covered with water, and having trees and shrubs.
Swelling	The expansion of an ion exchange bed which occurs when the reactive groups on the resin are converted from one form to another. This property is reversible and indeed, some resins shrink in the exhausted state.
Synergism	The combined action of several chemicals, which produces a total effect greater than the effects of the chemicals separately.
Synoptic Sites	Sites sampled during a short-term investigation of specific water-quality conditions during selected seasonal or hydrologic conditions, to provide improved spatial resolution for critical water-quality conditions.

Tailings	Rock that remains after processing ore to remove the valuable minerals.
Tannin	A naturally occurring substance in wood, grapeskins, seeds and stems. Is primarily responsible for the basic bitter component in wines. Acts as a natural preservative, helping the development and, in the right proportion, balance of the wine. Considered a pollutant when present in excess.
Tarn	A relatively small and deep, steep-sided lake or pool occupying an ice-gouged basin amid glaciated mountains.
Taxa Richness	See Species richness.
Taxon (plural taxa)	Any identifiable group of taxonomically related organisms.
TCE (Trichloroethylene)	A toxic volatile organic chemical typically used as an industrial solvent.
TDS	TDS stands for total dissolved solids, and represents the total concentration of dissolved substances in water. TDS is made up of inorganic salts, as well as a small amount of organic matter. Common inorganic salts that can be found in water include calcium, magnesium, potassium and sodium, which are all cations, and carbonates, nitrates, bicarbonates, chlorides and sulfates, which are all anions. Cations are positively charged ions and anions are negatively charged ions.
Tectonic Activity	Movement of the Earth's crust resulting in the formation of ocean basins, continents, plateaus, and mountain ranges.
Terminal Moraine	The endmoraineextending across a glacial plain or valley as an arcuate or crescent ridge that marks the farthest advance or maximum extent of a glacier.
Terrane	Area or surface over which a particular rock type or group of rock types is prevalent.
Terrestrial	Pertaining to, consisting of, or representing the Earth.
Tertiary	Treated sewage- The third phase of treating sewage that removes nitrogen and phosphorus before it is discharged.
Tertiary Treatment	Advanced cleaning of wastewater that goes beyond the secondary or biological stage, removing nutrients such as phosphorus, nitrogen, and most BOD and suspended solids.
Tertiary Wastewater Treatment	Selected biological, physical, and chemical separation processes to remove organic and inorganic substances that resist conventional treatment practices; the additional treatment of effluent beyond that of primary and secondary treatment methods to obtain a very high quality of effluent. The complete wastewater treatment process typically involves a three-phase process: (1) First, in the primary wastewater treatment process, which incorporates physical aspects, untreated water is passed through a series of screens to remove solid wastes; (2) Second, in the secondary wastewater treatment process, typically involving biological and chemical processes, screened wastewater is then passed a series of holding and aeration tanks and ponds; and (3) Third, the tertiary wastewater treatment process consists of flocculation basins, clarifiers, filters, and chlorine basins or ozone or ultraviolet radiation processes.
TH	Total Hardness. The sum of calcium and magnesium hardness, expressed as a calcium carbonate equivalent.
Thermal Loading	Amount of waste heat discharged to a water body.
Thermal Pollution	A reduction in water quality caused by increasing its temperature, often due to disposal of waste heat from industrial or power generation processes.
Thermoelectric Power	Electrical power generated by use of fossil-fuel (coal, oil, or natural gas),geothermal, or nuclear energy.
Thermoelectric Power Water Use	Water used in the process of the generation of thermoelectric power. Power plants that burn coal and oil are examples of thermoelectric-power facilities.
Thermokarst	An irregular land surface formed in apermafrostregion by melting ground ice and a subsequent settling of the ground.
Thin	Film Composite Membrane (TFC)-Reverse osmosis membrane produced with polyamide-based polymer. It is resistant to bacteria and can withstand a wide pH range. However, it cannot tolerate chlorine.
THM	Trihalomethanes. Toxic chemical substances that consist of a methane molecule and one of the halogen elements fluorine, bromine, chlorine and iodine attached to three positions of the molecule. They usually have carcinogenic properties.
Throughput Volume	The amount of solution passed through an exchange bed before exhaustion of the resin is reached.
Tidal Flat	An extensive, nearly horizontal, tract of land that is alternately covered and uncovered by the tide and consists of unconsolidated sediment.
Tide	The rhythmic, alternate rise and fall of the surface (or water level) of the ocean, and connected bodies of water, occurring twice a day over most of the Earth, resulting from the gravitational attraction of the Moon, and to a lesser degree, the Sun.
Tier 1 Sediment Guideline	Threshold concentration above which there is a high probability of adverse effects on aquatic life from sediment contamination, determined using modified U.S. Environmental Protection AgencyUSEPA(1996) procedures.
Tile Drain	A buried perforated pipe designed to remove excess water from soils.
Till	Predominantly unsorted and unstratified drift, deposited directly by and underneath a glacier without subsequent reworking by meltwater, and consisting of a heterogeneous mixture of clay, silt, sand, gravel, and boulders.
Tinaja	A pocket of water developed below a waterfall; a term used in the Southwestern United States; used loosely to mean a temporary pool.
Tissue Study	The assessment of concentrations and distributions of trace elements and certain organic contaminants in tissues of aquatic organisms.
Titration	An analytical technique to determine how much of a substance is present in a water sample by adding another substance and measuring how much of that substance must be added to produce a reaction.
Tolerant Species	Those species that are adaptable to (tolerant of) human alterations to the environment and often increase in number when alterations occur.
Topography	The general configuration of a land surface or any part of the Earth's surface, including its relief and the position of its natural and man-made features.
Total Acidity	The total of all forms of acidity, including mineral acidity, carbon dioxide, and acid salts. Total acidity is usually determined by titration with a standard base solution to the phenolphthalein endpoint (pH 8.3).
Total Alkalinity	The alkalinity of a water as determined by titration with standard acid solution to the methyl orange endpoint (pH approximately 4.5); sometimes abbreviated as M alkalinity. Total alkalinity includes many alkalinity components, such as hydroxides, carbonates, and bicarbonates.
Total Chlorine	The total amount of chlorine is a solution, which includes the combined chlorine as well as the free available chlorine.
Total Concentration	Refers to the concentration of a constituent regardless of its form (dissolved or bound) in a sample.
Total DDT	The sum of DDT and its metabolites (breakdown products), including DDD and DDE.
Total Dissolved Solids	The weight of solids per unit volume of water which are in true solution, usually determined by the evaporation of a measured volume of filtered water, and determination of the residue weight. TDS is expressed as ppm per unit volume of water. An electrical conductivity test provides only an estimate of the TDS since non-conductive substances cannot be measured by electrical means.
Total Hardness	The sum of all hardness components in a water, expressed as their equivalent concentration of calcium carbonate. Primarily due to calcium and magnesium in solution, but may include small amounts of metals such as iron which can act like calcium and magnesium in certain reactions. These minerals are scale forming, affect taste and color of certain foods and react with soap to form insoluble soap curds.
Total Head	The height above a datum plane of a column of water. In a ground-water system, it is composed of elevation head and pressure head.
Total Organic Carbon	The measurement of carbon dioxide produced from organics when a water sample is atomized into a combustion chamber. The amount of carbon covalently bound in organic compounds in a water sample.
Total Solids	The weight of all solids, dissolved and suspended, organic and inorganic, per unit volume of water; usually determined by the evaporation of a measured volume of water at 105 degrees Celsius in a pre-weighed dish.
Toxic Water Pollutants	Compounds that are not naturally found in water at the given concentrations and that cause death, disease, or birth defects in organisms that ingest or absorb them.
Trace Element	A chemical element that is present in minute quantities in a substance.
Tracer	A stable, easily detected substance or a radioisotope added to a material to follow the location of the substance in the environment or to detect any physical or chemical changes that it undergoes.
Trade Winds	A system of easterly winds that dominate most of the tropics. A major component of the general circulation of the atmosphere.
Transit-time Ultrasonic Meter	Transit-time ultrasonic water meters send ultrasound signals into the flow using transducers that are either clamped onto or inserted into the pipe at two locations. The difference between the time it takes for sound to travel upstream and downstream between the two sensors is directly proportional to flow velocity.
Transmissivity	The rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of an aquifer under a unit hydraulic gradient. It equals the hydraulic conductivity multiplied by the aquifer thickness.
Transmissibility (groundwater)	The capacity of a rock to transmit water under pressure. The coefficient of transmissibility is the rate of flow of water, at the prevailing water temperature, in gallons per day, through a vertical strip of the aquifer one foot wide, extending the full saturated height of the aquifer under a hydraulic gradient of 100-percent. A hydraulic gradient of 100-percent means a one foot drop in head in one foot of flow distance.
Transmission Lines	Pipelines that transport raw water from its source to a water treatment plant.
Transmissivity	The ability of an aquifer to transmit water.
Transpiration	Process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores.
Treatment Plant	A structure built to treat wastewater before discharging it into the environment.
Triazine Herbicide	A class of herbicides containing a symmetrical triazine ring (a nitrogen-heterocyclic ring composed of three nitrogens and three carbons in an alternating sequence). Examples include atrazine, propazine, and simazine.
Triazine Pesticide	See Triazine herbicide.
Tributary	A smaller river or stream that flows into a larger river or stream. Usually, a number of smaller tributaries merge to form a river.
Trickling Filter	A wastewater treatment unit that contains medium material with bacteria. The stream of wastewater is trickled over the medium and the bacteria break down the organic wastes. Bacteria are collected on the filter medium.
Trihalomethanes (THM's)	A group of organic chemicals to known to be carcinogenic in more than trace amounts which are produced from chlorination. They reduce the germicidal activity of chlorine in alkaline water.
Tritium	A radioactive form of hydrogen with atoms of three times the mass of ordinary hydrogen; can be used to determine the age of water.
Tropical Cyclone	A cyclone that originates over the tropical oceans. Tropical cyclones are classified according to their intensity and windspeed and, when fully mature, are characterized by extremely high-speed winds and torrential rains. In the United States, tropical cyclones that have windspeeds greater than 40 miles per hour are classified as tropical storms, and tropical cyclones that have windspeeds of 74 miles per hour or more are classified as hurricanes. See also Cyclone.
Troposphere	Lowest 6 to 12 miles of the atmosphere, characterized by a general decrease in temperature with height, appreciable water content, and active weather processes.
Trough (ground water)	A linear structural depression that extends laterally over a distance. Although it is less steep than a trench, a trough can be a narrow basin or a geologic rift. These features often form at the rim of tectonic plates.
Trough (meteorological)	An elongated (extended) region of relatively low atmospheric pressure, often associated with fronts.[1] Troughs may be at the surface, or aloft, or both under various conditions. Most troughs bring clouds, showers, and a wind shift, particularly following the passage of the trough. This results from convergence or "squeezing" which forces lifting of moist air behind the trough line.
TS	Total Solids. The weight of all present solids per unit volume of water. It is usually determined by evaporation. The total weight concerns both dissolved and suspended organic and inorganic matter.
Tube Settler	Device using bundles of tubes to let solids in water settle to the bottom for removal by sludge.
Tundra	A vast, nearly level, treeless plain of the arctic and subarctic regions. It usually has a marshy surface which supports mosses, lichens, and low shrubs, underlain by mucky soils andpermafrost.

UL	Underwriters Laboratories (UL) is a global safety science company, the largest and oldest independent testing laboratory in the United States. Underwriters Laboratories tests the latest products and technologies for safety before they are marketed around the world.
Ultra	Violet (UV) -enhanced oxidation such as UV/ ozone, UV/ hydrogen, UV/air
Ultra Violet Oxidation	A process using extremely short wave-length light that can kill micro-organisms (disinfection) or cleave organic molecules (photo oxidation) rendering them polarized or ionized and thus more easily removed from the water.
Ultrafiltration	A membrane type system that removes small colloids and large molecules from solutions. Ultrafiltration removes particles in size range between 0.002 to 0.1 micron range. The process falls between reverse osmosis and microfiltration as far as the size of particles removed is concerned.
Ultrapure Water	No standards exist describing ultrapure water though it is not considered to be sterile. It is water that has been deionized and provides high resistivity and contains no organics.
Ultrasonic Meter	Ultrasonic meters implement sound waves to measure water speed and convert findings into volume.
Ultraviolet Light	Radiation having a wave length shorter than 4000 angstroms (visible light) down to 100 angstroms on the border of the x-ray region. Ultraviolet light is used as a disinfectant.
Un Ionized	The neutral form of an ionizable compound (such as an acid or a base).
Un Ionized Ammonia	The neutral form of ammonia-nitrogen in water, usually occurring as NH4OH. Un-ionized ammonia is the principal form of ammonia that is toxic to aquatic life. The relative proportion of un-ionized to ionized ammonia (NH4+) is controlled by water temperature and pH. At temperatures and pH values typical of most natural waters, the ionized form is dominant.
Unconfined Aquifer	Anaquiferwhose upper surface is a water table free to fluctuate under atmospheric pressure.
Unconsolidated Deposit	Deposit of loosely bound sediment that typically fills topographically low areas.
Underground Water	Subsurface water in the unsaturated and saturated zones. See alsoGround water
Understory	A foliage layer lying beneath and shaded by the main canopy of a forest.
Unloading	The release of the contaminant that was captured by a filter medium.
Unsaturated Zone	The zone between the land surface and the water table.
Up Flow	An upward flow of water.
UP Water	Ultra pure water creation demands a specialized way of working. A number of techniques are used amongst others; membrane filtration, ion exchanges, sub micron filters, ultra violette and ozone systems. The produced water is extremely pure and contains none to very low concentrations of salts, organic/ pyrogen components, oxygen, suspended solids and bacteria.
Upflow	The operation of an ion exchange unit in which solutions are passed in at the bottom and out at the top of the container.
Upgradient	Of or pertaining to the place(s) from which ground water originated or traveled through before reaching a given point in an aquifer.
Upland	A general term for nonwetland; elevated land above low areas along streams or between hills; any elevated region from which rivers gather drainage.
Uranium (U)	A heavy silvery-white metallic element, highly radioactive and easily oxidized. Of the 14 known isotopes of uranium, U238 is the most abundant in nature.
Urban Runoff	Water from city streets domestic properties that carries pollutants into the sewer systems and receiving waters.
Urban Site	A site that has greater than 50 percent urbanized and less than 25 percent agricultural area.
UV	Ultra Violet. Radiation that has a wavelength shorter than visible light. It is often used to kill bacteria and destroy ozone.

Vapor	The gaseous phase of substances such as water.
Vaporize	Conversion of a liquid into vapor.
Vascular Plant	A plant composed of or provided with vessels or ducts that convey water or sap. A fern is an example of this type of plant.
Velocity Meter	These meters measure the speed of the water as it passes through the device. From there, they convert the velocity of water through the specific volume of the meter and the user receives a measurement of water consumption in cubic feet or gallons.
Venturi	A system for speeding the flow of the fluid, by constricting it in a cone shape tube. In the restriction the fluid must increase its velocity reducing its pressure and producing a partial vacuum. As the fluid leave the constriction, its pressure increase back to the ambient or pipe level.
Vernal Pool	A small lake or pond that is filled with water for only a short time during the spring.
Virus	The smallest form of life known to be capable of producing disease or infection, usually considered to be of large molecular size. They multiply by assembly of component fragments in living cells, rather than be cell division, as do most bacteria. Being parasitic infectious microbes, they are much smaller than bacteria.
Viruses	The smallest life forms known, that are not cellular in nature. They live inside the cells of animals, plants and bacteria and often cause disease. They are made up of a chromosome surrounded by a protein shell.
Viscosity	The syrupiness of water and it determines the mobility of the water. When the temperature rises, the viscosity degrades; this means that water will be more mobile at higher temperatures.
VOC	Volatile Organic Compound. Synthetic organic compounds which easily vaporize and are often carcinogenic.
Void Area	The space between the resin beads in an ion exchange bed or the space between the particles of filter media bed. Also can be defined as the space between the chunks of salt in a brine tank.
Volatile Organic Compounds (VOCs)	Organic chemicals that have a high vapor pressure relative to their water solubility. VOCs include components of gasoline, fuel oils, and lubricants, as well as organic solvents, fumigants, some inert ingredients in pesticides, and some by-products of chlorine disinfection.

Wastewater	Water that has been used in homes, industries, and businesses that is not for reuse unless it is treated.
Wastewater Infrastructure	The plan or network for the collection, treatment, and disposal of sewage in a community.
Wastewater-Treatment Return Flow	Water returned to the environment by wastewater-treatment facilities.
Wasteway	A waterway used to drain excess irrigation water dumped from the irrigation delivery system.
Water Budget	An accounting of the inflow to, outflow from, and storage changes of water in ahydrologic unit.
Water Column	An imaginary column extending through a water body from its floor to its surface.
Water Column Studies	Investigations of physical and chemical characteristics of surface water, which include suspended sediment, dissolved solids, major ions, and metals, nutrients, organic carbon, and dissolved pesticides, in relation to hydrologic conditions, sources, and transport.
Water Conditioning	Virtually any form of water treatment designed to improve the quality of water, by neutralization, inhibition or removal of undesirable substances.
Water Content Of Snow	Amount of liquid water in the snow at the time of observation. Water equivalent of snow.
Water Cycle	The circuit of water movement from the oceans to the atmosphere and to the Earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transportation.
Water Demand	Water requirements for a particular purpose, such as irrigation, power, municipal supply, plant transpiration, or storage.
Water Distribution System	An example of a water distribution system: a pumping station, a water tower, water mains, fire hydrants, and service lines. A water distribution system is a part of a water supply network with components that carry potable water from a centralized treatment plant or wells to consumers to satisfy residential, commercial, industrial and fire fighting requirements. Components of a water distribution system can include a pumping station, water tower, water mains, fire hydrants, service lines, and water meters.
Water Exports	Artificial transfer (by pipes or canals) of freshwater from one region or subregion to another.
Water Gap	A deep, narrow pass in a mountain ridge through which a stream flows.
Water Hammer	The shock wave produced by the abrupt change of water flow through a piping system. Water hammer produces an instantaneous multiple increase in the pressure normal to the system. The installation of a water hammer arrestor will absorb these shock waves.
Water Imports	Artificial transfer (by pipes or canals) of freshwater to one region or subregion from another.
Water Meter Register	The water meter register is a lot like the mileage odometer on your car. The numbers keep a running total of all the water that has passed through the meter. Water volume expressed in either cubic feet or gallons. The register shown here indicates that 10 gallons of water has passed through this meter.
Water Monitoring	The process of constant control of a body of water by means of sampling and analyses.
Water Pollution	The presence in water of enough harmful or objectionable material to damage water quality.
Water Quality	A term used to describe the chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose.
Water Quality Criteria	Specific levels of water quality which, if reached, are expected to render a body of water unsuitable for its designated use. Commonly refers to criteria established by the U.S. Environmental Protection Agency. Water-quality criteria are based on specific levels of pollutants that would make the water harmful if used for drinking, swimming, farming, fish production, or industrial processes.
Water Quality Guidelines	Specific levels of water quality which, if reached, may adversely affect human health or aquatic life. These are nonenforceable guidelines issued by a governmental agency or other institution.
Water Quality Standards	State-adopted and U.S. Environmental Protection Agency-approved ambient standards for water bodies. Standards include the use of the water body and the water-quality criteria that must be met to protect the designated use or uses.
Water Recycling	Using water again for the same or another process step, after a small form of purification is applied.
Water Rights	Legal rights to the use of water.See alsoRiparian rights.
Water Softening	The reduction or removal of calcium and magnesium ions which are the principle cause of hardness in water.
Water Solubility	The maximum possible concentration of a chemical compound dissolved in water.
Water Storage Pond	An impound for liquid wastes designed to accomplish some degree of biochemical treatment.
Water Supply System	The collection, treatment, storage, and distribution of water from source to consumer.
Water System	A river and all its branches.
Water Table	The top of the water surface in the saturated part of an aquifer.
Water Use	Water that is used for a specific purpose, such as for domestic use, irrigation, or industrial processing. Water use pertains to human's interaction with and influence on the hydrologic cycle, and includes elements, such as water withdrawal from surface- and groundwater sources, water delivery to homes and businesses, consumptive use of water, water released from wastewater-treatment plants, water returned to the environment, and instream uses, such as using water to produce hydroelectric power.
Water Year	A continuous 12-month period selected to present data relative to hydrologic or meteorological phenomena during which a complete annualhydrologic cyclenormally occurs. The water year used by the U.S. Geological Survey runs from October 1 through September 30, and is designated by the year in which it ends.
Watershed	The land area that drains water to a particular stream, river, or lake. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge.
Watthour (Wh)	An electrical energy unit of measure equal to one watt of power supplied to, or taken from, an electrical circuit steadily for one hour.
Weather	State of the atmosphere at any particular time and place.
Weathering	Process whereby earthy or rocky materials are changed in color, texture, composition, or form (with little or no transportation) by exposure to atmospheric agents.
Weighted Mean	A value obtained by multiplying each of a series of values by its assigned weight and dividing the sum of these products by the sum of the weights. In the ordinary arithmetic mean, each value is assigned a weight of 1.
Weir	A spill over device used to measure or control water flows.
Well	A deep hole with the purpose to reach underground water supplies.
Well (water)	An artificial excavation put down by any method for the purposes of withdrawing water from the underground aquifers. A bored, drilled, or driven shaft, or a dug hole whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies or oil, or to store or bury fluids below ground.
Wet Air Oxidation	Catalytic wet air oxidation (where air is used as the oxidant)
Wetland	A distinct ecosystem that is flooded by water, either permanently or seasonally, where oxygen-free processes prevail. The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil.
Wetland Function	A process or series of processes that take place within a wetland that are beneficial to the wetland itself, the surrounding ecosystems, and people.
Wettability	The relative degree to which a fluid will spread into solid surface in the presence of other immiscible fluids.
Willow Carr	A pool, or wetland dominated by willow trees or shrubs.
Withdrawal	Water removed from the ground or diverted from a surface-water source for use. Also refers to the use itself; for example, public-supply withdrawals or public-supply use.

Karst	A type of topography that results from dissolution and collapse of carbonate rocks such as limestone, dolomite, and gypsum, and that is characterized by closed depressions or sinkholes, caves, and underground drainage.
KDF	A water treatment media employing copper and zinc alloy particulates which have a redox potential. KDF does not support the growth of bacteria and lasts up to twenty times longer than activated carbon. KDF 55 granules are effective in removing chlorine and other water-soluble heavy metals such as lead. KDF 85 is the choice for removing iron and hydrogen sulfide.
Kettle	A steep-sided hole or depression, commonly without surface drainage, formed by the melting of a large detached block of stagnant ice that had been buried in the glacial drift.
Kettle Lake	A body of water occupying a kettle, as in a pitted outwash plain or in a kettle moraine.
Kill	Dutch term for stream or creek.
Kilograin	A unit of weight; one thousand grains, 17100 ppm, or 0.1429 pounds.
Kilowatthour (KWH)	A power demand of 1,000 watts for one hour. Power company utility rates are typically expressed in cents per kilowatt-hour.
Kinetic Energy	Energy possessed by moving water.
Kinetic Rate Coefficient	A number that describes the rate at which a water constituent such as a biochemical oxygen demand or dissolved oxygen rises or falls.
Kinetics	The study of the relationships between temperature, motion, and the velocity of very small particles. It is used to describe the rate of ion exchange reactions.

Qualitative Water Assessment	Analyses of water used to describe the visible or aesthetic characteristics of water.
Quality Assurance	Evaluation of quality-control data to allow quantitative determination of the quality of chemical data collected during a study. Techniques used to collect, process, and analyze water samples are evaluated.
Quantitative Water Assessment	Use of analyses of water properties and concentrations of compounds and contaminants in order to define water quality.
Quartz Sleeve	Also called a quartz jacket, it is a clear, pure quartz sleeve that is installed around the high intensity ultraviolet lamp in an ultraviolet system. It retards less than 10 percent of the radiation dosage in contrast to the poorer results offered by glass.
Quicksilver Water	A solution of mercury nitrate used in gilding.

Xenobiotic	Any biological substance, displaced from its normal habitat; a chemical foreign to a biological system.
Xeriscaping	A method of landscaping that uses plants that are well adapted to the local area and are drought-resistant. Xeriscaping is becoming more popular as a way of saving water at home.
Xerophyte	A plant adapted for growth under dry conditions.
Xylene	A volatile organic chemical (VOC) commonly used in industry as a solvent.

Zeolite	Naturally occurring or synthetic hydrated sodium alumina silicate with ion exchange properties. Zeolites have been largely replaced with synthetic organic cation ion exchange resins. Modified Zeolites can be selectively charged with exchange minerals such as potassium and used to remove undesirable elements such as iron, hydrogen, sulfide, and manganese.
Zero Discharge Water	The principle of zero discharge is recycling of all industrial wastewater. This means that wastewater will be treated and used again in the process. Because of the water reuse wastewater will not be released on the sewer system or surface water.
Zeta Potential	An electro kinetic measurement which can be used for the control of coagulation processes.
Zooplankton	A type of heterotrophic plankton that range from microscopic organisms to large species, such as jellyfish. Zooplankton are found within large bodies of water, including oceans and freshwater systems. Zooplankton are drifting ecologically important organisms that are an integral component of the food chain.

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ParkUSA

Northwest Pipe Company

Headquarters

ParkUSA Texas Coastal

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Requests

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ParkUSA Northeast &
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