rainwater and stormwater: two sides of the same story?


“Rainwater harvesting” (RWH) and “stormwater catchment” are often used interchangeably referring to a wide range of practices that capture and utilize or infiltrate rainfall on a site, rather than funneling it into storm drains. In urban areas, unused and non infiltrated rainwater is simply stormwater in the making.

Stormwater consists of rainwater, snowmelt, and other water sources (such as water from hoses, industry or agriculture) that run across impervious surfaces and saturated soils into street gutters and storm drains, streams, rivers, and finally the ocean. Stormwater runoff picks up pollutants like trash, chemicals, car oils and lubricants, animal and human feces, and dirt/sediment that harm our streams, rivers, lakes, and coastal waters.

For many of us, the connection between rainwater and stormwater is an “Ah Ha!” moment.  Of course!  Stormwater, also called stormwater runoff, is rainwater that hasn’t been given the chance to infiltrate. Stormwater, also called stormwater runoff, comes from rainwater, snow melt or from over-spraying hoses which run across impervious surfaces, such as sidewalks, driveways, parking lots, streets, or saturated soil. Stomrwater flows across ground-level surfaces without infiltrating into the soil. The runoff picks up pollutants like trash, chemicals, car oils and lubricants, animal and human feces, and sediment that harm our streams, rivers, lakes, and coastal waters.

Stormwater is rainwater that is unmanaged at the source, and so must be managed further down the line by stormwater systems, which can become inundated and overflow in heavy rains. In areas with combined sewers, such as Sacramento and San Francisco, the overflow can also contain sewage. The EPA has designated stormwater as one of the greatest sources of water pollution in the United States.

Fortunately, Green Infrastructure, also known as Low Impact Development (LID), recognizes the importance of managing rainwater where it falls by capturing it for use in landscapiong, toilet flushing, clothes washing, commercial and industrial purposes. With appropriate filtration, rainwater can even serve potable water uses such as bathing and drinking.  Stormwater managers ranging from individuals to the Federal EPA recognize rainwater harvesting (RWH) as a key strategy for stormwater management.

Learn more about how to utilize rainwater harvesting and land management to quell stormwater runoff on our Green Infrastructure page.