As the intensity of development increases, so does the generation of nonpoint source water pollution, or polluted runoff . Polluted runoff may contain contaminants such as excess nutrients, heavy metals, or chemicals that are harmful to both human and animal health. Generally, a good indicator of development intensity in a given area is the level of impervious surface coverage by structures such as roads, driveways, parking lots and roofs. A growing body of scientific research is finding a direct relationship between impervious surface coverage in a watershed and water quality. When as little as 15 percent of land within a watershed is covered with impervious surfaces, studies show that stream water can become increasingly polluted without proper management measures in place. In highly sensitive areas, negative eff ects on the stream health begin when as little as 8 to 10 percent of the watershed has impervious cover. Th e quality of our streams, groundwater and ocean water can be affected by polluted runoff. Increasing coverage of impervious surfaces also limits the quantity of water fi ltering into the ground and recharging our groundwater, often used for drinking or for irrigation. Th us, local offi cials can do much to protect their water resources by considering the location, extent, drainage and maintenance of impervious surfaces at the community, watershed and individual site levels. Natural resource planning, site design and use of Best Management Practices (BMPs) form an effective approach to addressing the problem.