Ground water is a vast resource that underlies the earth's surface.
Nearly half of the U.S. population uses ground water for their drinking water source, including virtually all rural residents. In addition, ground water provides much of the water used for irrigation and for industry. On average, about 40 percent of the annual streamflow in the United States is comprised of ground water seepage, although in some areas more than three fourths of the average streamflow, including virtually all fair weather flow, comes from ground water seepage into streambeds Ground water conditions vary widely among regions based on differences in geology, climate, and topography. Ground water use varies with the demand of the local population and industrial and agricultural requirements. Several federal statutes have ground water components, although no single federal statute has been enacted to comprehensively address ground water quality protection.