paper argues that irrigated agriculture's impact on goundwater is another water quality concern that is rapidly growing in importance and well deserves our profession's attention and research efforts. Groundwater is now the source of 50% of U.S. drinking water supplies and 40% of irrigation withdrawals, with reliance on groundwater varying tremendously across regions. Irrigated agriculture is the largest single user of the nation's groundwater resources, accounting for 70% of annual groundwater use. Groundwater withdrawals are increasing at double the rate of increase for surface water use, with half a million new wells drilled each year (Henderson et al., p. 9). As a part of a broader research effort examining water markets, values, and quality in the western United States (Saliba, Bush, and Martin), this paper explores the potential roles of public regulations and private markets in water quality management. The discussion focuses on nitrates, pesticides, and dissolved solids, the three principal groundwater contaminants associated with irrigated agriculture.