Stormwater consists of rainwater and other water sources (such as water from hoses, industry or agriculture) that run across impervious surfaces and saturated soil into street gutters and storm drains, streams, rivers, and finally the ocean. It carries with it chemicals and toxins that are picked up along the way, becoming a source of pollution.
For many of us, the connection between rainwater and stormwater is an "Ah Ha!" moment. Of course! Stormwater is rainwater that has fallen on impervious surfaces (such as roofs, sidewalks, driveways, parking lots, streets) and is allowed to run freely, picking up pollutants and toxins, until it falls into a stormwater drain system, most often released into surface waters untreated. Stormwater is rainwater that has not been captured for use or infiltrated into permeable surfaces. Stormwater is rainwater that is unmanaged at the source, and so must be managed further down the line by stormwater systems. The EPA has designated stormwater as the greatest source of water pollution in the United States.
Fortunately, Low Impact Design/Development (LID) strategies recognize the importance of manageing rainwater where it falls by capturing it for use in landscapiong, toilet flushing, clothes washing, commercial and industrial purposes. With appropriate filtration dependant on end use, rainwater can even serve *real* potable water uses such as bathing and drinking. Stormwater managers ranging from individuals to the Federal EPA are utilizing rainwater harvesting (RWH) as a primary strategy for stormwater management.