Stormwater is the flow of water that results from precipitation which occurs immediately following rainfall. When a rainfall event occurs, some of the precipitation infiltrates into the soil surface, some is taken up by plants and some is evaporated into the atmosphere. The rest of the precipitation that runs off land surfaces and impervious areas is stormwater.
Stormwater deposited on impervious surfaces, such as rooftops, driveways, and parking lots cannot penetrate into the ground. This is known as stormwater runoff. While this runoff is flowing to a storm drain or a nearby waterway, it picks up pollutants along its path. Eventually that stormwater and all it carries flows into Biscayne Bay.