Water use in the State of Washington has evolved in the past century from meager domestic and stock water needs to the current complex requirements of domestic-water users, large irrigation projects, industrial plants, and numerous other uses such as fish habitat and recreational activities. Since 1950, the U.S. Geological Survey (USGS) has, at 5-year intervals, compiled data on the amount of water used in homes, businesses, industries, and on farms throughout the State. This water-use data, combined with other related USGS information, has facilitated a unique understanding of the effects of human activity on the State's water resources. As water availability continues to emerge as an important issue in the 21st century, the need for consistent, long-term water-use data will increase to support wise use of this essential natural resource. This report presents state and county estimates of the amount of public- and self-supplied water used for domestic, irrigation, livestock, aquaculture, industrial, mining, and thermoelectric power purposes in the State of Washington during 2005. Offstream fresh-water use was estimated to be 5,780 million gallons per day (Mgal/d). Domestic water use was estimated to be 648 Mgal/d or 11 percent of the total. Irrigation water use was estimated to be 3,520 Mgal/d, or 61 percent of the total. Industrial fresh-water use was estimated to be 520 Mgal/d, or 9 percent of the total. These three categories accounted for about 81 percent (4,690 Mgal/d) of the total of the estimated offstream freshwater use in Washington during 2005.