Stormwater runoff is precipitation (rain or snowmelt) that flows across the land. Stormwater may infiltrate into soil, discharge directly into streams, water bodies, or drain inlets, or evaporate back into the atmosphere.

 

In the natural environment, most precipitation is absorbed by trees and plants or permeates into the ground, which results in stable stream flows and good water quality.

 

In urban areas with impervious surfaces, rain that falls on a roof, driveway, patio or lawn runs off the surface more rapidly, picking up pollutants and then flows into storm drains that discharge into the closest stream, ultimately making it's way to the Chesapeake Bay.