Stormwater is rainwater or snowmelt that, instead of seeping into the earth, "runs off" via gutters, storm drains and ditches into creeks, streams, rivers, lakes, and the ocean.

Environmental Concern

Although it is a necessary part of the natural water cycle, stormwater can also be an environmental concern. As stormwater flows over the land, it collects contaminants such as oil and grease from roadways, pesticides, and fertilizers from lawns, sediment from construction sites, and discarded trash, which can degrade water quality and the health of surrounding plants and animals. It is estimated that 70% of the water pollution in the United States comes from stormwater and other indirect discharges collectively known as "non-point" pollution sources.

Municipal Storm Sewers

Municipal storm sewers, also known as storm drains, are separate from the sanitary sewer system. They do not treat stormwater but rather work to convey the stormwater off the streets directly to the nearest stream or creek, as storm drains are designed to quickly remove runoff from streets to help prevent flooding. These also means that anytime a person might pour into or dispose of anything into a storm drain, it all goes directly into our lakes the next time it rains.

Quantity of Stormwater

The quality of stormwater runoff is only one half of the stormwater picture; the quantity of stormwater runoff poses its own problems. Increased development brings more streets, parking lots, rooftops, and other surfaces that shed water instead of absorbing it. One inch of rain falling on a one-acre parking lot produces 16 times more runoff than the same inch of rain falling on a one-acre meadow. Localized urban flooding, erosion, and the souring of streambeds are some impacts caused by increased stormwater runoff quantity.