A stormwater drain is designed to convey excess rain water, subsurface water, condensate or cooling water away from the building to prevent backflow into the building and water accumulating around footings and foundations. This water is channeled to a discharge point.
Stormwater drains are often operated independently from sewerage systems. The separation of stormwater drains from sanitary sewers helps to prevent sewage treatment plants becoming overwhelmed by the huge influx of water during a rainstorm, which can result in untreated sewage being discharged into the environment.
Stormwater is of concern for two main issues: volume and timing of runoff water (flood control and water supply) and potential contamination of water.