Once rainwater hits the ground it becomes classified as stormwater, and will tend to flow towards the lowest point in an area. Runoff that is not immediately absorbed into the ground, or that falls onto impervious surfaces, must be allowed to flow away from existing structures and towards designated bodies of water to prevent flooding. Stormwater drainage products are commonly used to develop and maintain storm sewer infrastructures through the use of storm-water inlets and stormwater management products.