C. L. Appel D. W. Litke 1989 Water-use data was collected for the State of Colorado as part of the U.S. Geological Survey 's National Water-Use Information Program. An estimated 20,800 million gal/day of water were used in Colorado during 1985. 89% came from surface water sources and 11% came from groundwater sources. Public supply systems provided 4% of all water used in Colorado during 1985, but provided 80% of all commercial, domestic, and industrial water used. An estimated 4,840 million gal/day of water were consumed during 1985; return flows amounted to 16,000 million gallons per day. Of all water used, 60% was used for irrigation, 35% for hydroelectric power generation, and the remaining 5% for commercial, domestic, industrial, livestock, mining, and other uses. The most water was used in Montrose (3,260 million gal/day), Mesa (1,950 million gal/day), and Gunnison (1,520 million gal/day) Counties. The predominant water uses in these counties were hydroelectric power and irrigation. (USGS) application/pdf 10.3133/wri884101 en U.S. Geological Survey, Estimated use of water in Colorado, 1985 reports