Stormwater runoff from urban areas delivers pollutants — including pathogens, nutrients, sediment, and heavy metals — to our streams, lakes, and beaches. In cities with combined sewer systems, high stormwater flows also can send untreated sewage into our waters. By retaining rainfall from small storms, LID practices reduce stormwater discharges. In turn, lower discharge volumes translate into reduced combined sewer overflows and lower pollutant loads.
Water quality can affect environmental health, local economy, and overall quality of life. Poor water quality can lead to beach closures, decreased recreational and commercial fishing opportunities, and poor drinking water. Maintaining and enhancing water quality is an important component of stormwater management. In addition to volume reduction, LID practices often provide water quality treatment of runoff, which can take up a lot of resources in relation to traditional stormwater systems. Filtration, combined with runoff volume reduction, significantly reduces pollutant loads that would otherwise flow to a receiving stream and eventually pollute our lakes and rivers.