When rain, snow, or another type of precipitation hits a surface, it becomes stormwater. In natural landscapes, stormwater gets soaked up into the ground or falls directy into waterbodies. However, when rain or water hit hard surfaces like pavement, sidewalks, and roofs it creates stormwater runoff. On its journey, stormwater picks up and transports many of the pollutants it encounters, which are NOT treated before draining directly to the rivers, streams, and lakes that hold our drinking water. These pollutants include sediment, pet wastes, pesticides, fertilizers, automobile fluids (such as oil, gasoline, and antifreeze), yard wastes, cigarette butts, litter, and more. By carrying all these different kinds of pollution into our waterways, stormwater runoff itself becomes a pollutant!
In addition to stormwater pollutants, stormwater quantity can also become an issue when too much water moves too quickly over a landscape. This can cause increased erosion, flooding, and drastic temperature change in waterways. Urban areas are especially susceptible to stormwater runoff because of the large amounts of impervious surface. The infographic below shows how the amount of runoff increases as the amount of impervious surface increases.