Stormwater management is the process of controlling runoff from rainfall or snow melt that is generated from impervious surfaces like parking lots, driveways, and roof tops. In Roanoke County, the stormwater system is separate from the sanitary sewer system. Stormwater flows directly from streets and gutters into the area's streams and rivers without any treatment before its discharge. Stormwater runoff also transports the pollutants it collects from these hard surfaces, such as motor oil, household cleaners, fertilizers, and other materials, that may negatively impact water quality of the receiving waters.