Periodic assessments of water use in Iowa are needed to understand and manage the demands for the available water resources. This report summarizes where, how much, and for what purposes water was used in Iowa during 1985. The data are presented for the following categories: agricultural, self-supplied commercial, self-supplied domestic, self-supplied industrial, irrigation, mining, power generation (excluding hydroelectric plants), and public-water supply. The water-use data are further categorized by county, hydrologic unit subregion, and major aquifer system. During 1985, a total of 1,010,000 million gallons was estimated to have been withdrawn from Iowa's surface- and ground-water resources. Of this, 76 percent was withdrawn from surface-water sources and 24 percent from ground-water sources. Power generation was the largest water-use category, withdrawing 66 percent of the total withdrawals; 99 percent was from surface-water sources. Public-water supply was the second largest water-use category and accounted for 13 percent of total withdrawals; 74 percent was from ground-water sources. Self-supplied industries withdrew 7 percent of the total water use and agricultural withdrawals were 6 percent of the total water use. The remaining 8 percent was accounted for by irrigation (3 percent), self-supplied domestic (2 percent), mining (2 percent), and self-supplied commercial (1 percent) water users. The largest estimated water use occurred in Woodbury County where 201,000 million gallons was withdrawn. Pottawattamie County had the second largest water use with 182,000 million gallons. Other counties with significant withdrawals were Allamakee (74,900 million gallons), Muscatine (63,900 million gallons), and Clinton (62,300 million gallons). Power generation plants are in each of these counties. Surface-water withdrawals were most intensive along the Mississippi and Missouri Rivers. Nearly 80 percent of the surface water used in the State was by power generation plants on the border rivers. Surficial aquifers were the source of 60 percent of the ground-water withdrawals. The remaining 40 percent was withdrawn from the following aquifers: Silurian-Devonian, 14 percent; Cambrian-Ordovician, 13 percent; Dakota, 8 percent; and Mississippian-Pennsylvanian, 5 percent. It was estimated that 17 percent of the total surface water and ground water withdrawn was consumed.