Blaine County in south-central Idaho experienced a 40-percent population growth-from 13,000 to more than 20,000 people-from 1990 to 2000. Between April 1, 2000, and July 1, 2005, the county population increased by about 11.5 percent (U.S. Census Bureau, 2007). In addition to permanent residents, thousands of people annually visit Blaine County for winter and summer recreation. Most population growth and recreational use is in the northernmost part of the county in the Wood River Valley. The entire population of the valley depends on ground water for domestic supply, either from privately owned or municipal-supply wells; surface water is used for recreation and irrigation.