An environmental assessment of United States drinking water watersheds

There is an emerging recognition that natural lands and their conservation are important elements of a sustainable drinking water infrastructure. We conducted a national, watershed-level environmental assessment of 5,265 drinking water watersheds using data on land cover, hydrography and conservation status. Approximately 78% of the conterminous United States lies within a drinking water watershed. The typical drinking water watershed had a high percentage of natural vegetation ((x)\tilde] \tilde{x}  = 77%) but a low percentage of it was set aside for conservation ((x)\tilde] \tilde{x}  = 3%). Median percentage values for urban and agriculture were 5 and 8%, respectively. Between ca. 1992 and ca. 2001, approximately 23% of the drinking water watersheds lost at least 1% of their natural vegetation, and approximately 9% of the watersheds had at least a 1% increase in the amount of urban land. Loss of natural vegetation was common in nearly all areas of the country, but also concentrated in the Ohio River and Southeast hydrologic regions. Urbanization was concentrated in the eastern United States, primarily in the Mid-Atlantic and Southeast hydrologic regions.