In Virginia, groundwater is an important source of private and public water supplies. In fact, in 60 of Virginia's 95 counties, the majority of households obtain water from private wells and springs (see Figure 1). For 38 counties, groundwater is the sole source for public water supplies, and another 16 counties depend on groundwater to obtain more than 50 percent of their water for public supplies. Overall, more than one-third of Virginia's almost 6.4 million residents depend on groundwater. Agriculture, an important part of Virginia's economy, maintains its high productivity, partially by using groundwater. According to U.S. Geological Survey estimates for the year 1990, almost 22 percent of the 36 million gallons of fresh water source used per day for crop irrigation in Virginia was derived from groundwater.