Total water use in the United States for 2000 was determined from estimates of water withdrawals for the eight categories of public supply, domestic, irrigation, livestock, aquaculture, industrial, mining, and thermoelectric power. Total freshwater and saline-water withdrawals for 2000 were estimated to be 408,000 million gallons per day (Mgal/d), or 457,000 thousand acre-feet per year. Freshwater withdrawals were 85 percent of the total, and the remaining 15 percent was saline water. Estimates of withdrawals by source indicate that for 2000, total surface-water withdrawals were 323,000 Mgal/d, or 79 percent of the total withdrawals for all categories of use. About 81 percent of surface water withdrawn was freshwater. Total ground-water withdrawals were 84,600 Mgal/d, of which 99 percent was freshwater. Nearly all (98 percent) saline-water withdrawals were from surface water.
Here's a bar chart showing water-use trends over time.