Impervious surfaces are mainly constructed surfaces (e.g., rooftops, sidewalks, roads, and parking lots) covered by impenetrable materials such as asphalt, concrete, brick, and stone. These materials seal surfaces, repel water and prevent precipitation and melted snow and ice from infiltrating soils. Soils compacted by urban development are also highly impervious. Impervious surfaces allow many types of pollutants, derived from a variety of sources, to accumulate upon them. Many of these pollutants are subsequently washed into water bodies by stormwater runoff which can severely degrade water quality. This type of pollution, known as nonpoint-source water pollution, is linked to land-use activities. Water-quality problems increase with increased imperviousness and the intensity of land use. .