Water-use data during calendar year 1995 was compiled for the 78 municipios of the Commonwealth of Puerto Rico. Eight offstream water-use categories were considered during the study: public supply, wastewater treatment discharges, domestic, industrial, mining, thermoelectric power, livestock, and irrigation. Three instream water-use categories were considered: hydroelectric power, saline water used at thermoelectric power plants, and reservoir evaporation. Freshwater withdrawals for offstream use from surface- and ground-water sources in Puerto Rico were estimated to be 566 million gallons per day. The largest amount of freshwater withdrawn was 431 million gallons per day for public supply. Total discharge from public wastewater treatment facilities was reported as 185 million gallons per day. Fresh surface- and ground-water withdrawals for domestic and industrial self-supplied facilities were estimated to be about 19 million gallons per day. Mining activities, which in Puerto Rico are mostly limited to the production of sand and gravel, withdrew about 4.2 million gallons per day of freshwater. Livestock activities used 6.3 million gallons per day from surface- and ground-water sources to meet the water needs of the 12.1 million animals counted in the 1992 Census of Agriculture in Puerto Rico. Self-supplied ground-water withdrawals for thermoelectric facilities were estimated to be 2.2 million gallons per day. Freshwater withdrawals for irrigation purposes were estimated to be 103 million gallons per day, or approximately 18 percent of all offstream freshwater withdrawals. Instream freshwater withdrawals by hydroelectric facilities were 349 million gallons per day. Reservoir evaporation is considered to be a consumptive use associated with the storage of water. The evaporation from 15 reservoirs in Puerto Rico was estimated to average about 23,900 acre-feet from a total reservoir surface area of 6,900 acres. The largest amount of withdrawals was 2,260 million gallons per day of saline water (instream use) for thermoelectric power.