Electric power.

The U. S. uses more water to produce electricity than for any other purpose. Electricity heats and cool buildings, drives trains, melts metals. Water helps generate power through two difference processes thermoelectric and hydroelectric. Thermnoelectric plants, which convert water into steam by heating it with fossil or nuclear fuels, provide nearly 90 percent of U.S. electric power. Though the plants guzzle 131 billion gallons of water each day, only 3 percent of that is actually consumed; the remainder is poured back into lakes and rivers. Though never leaving the stream and thus not considered a "withdrawal," far more water is needed for hydro­electric power, which provides rough­ly 10 percent of U. S. electricity. Water from dammed reservoirs pro­vides the gravity-driven force that turns turbines to energize dynamos.

Agriculture.

Practiced extensively in the West, irrigation brings cotton to Arizona, potatoes to Idaho, tomatoes to Cali­fornia. About 40 percent of U. S. water withdrawals are spent on irrigation; in some areas, more than 90 percent. Though it is seen mainly in the West, a growing number of south-eastern farmers are turning to irrigation to increase yields and fight drought. Irrigated lands are dis­proportionately productive: Only about 5 percent of U. S. farmlands are irrigated, but they produce 20 percent of the value of farm products.

Large government subsidies have encouraged irrigated farming since the early 1900s. More recently water shortages, decreased subsidies, and rising costs of pumping water have pushed farmers to adopt more effi­cient irrigation practices – thus curb­ing western water use.

Farm animals and aquaculture account for only a small proportion – about 3 percent – of agricultural water use. Since 1980 a growing fish-farm industry has doubled demand, traditionally limited to livestock.

Industry.

It takes less water to forge steel, make paper, manufacture paint, and pro­duce plastic than it used to. While U. S. output has quadrupled since 1950, industrial water use has dropped by 19 percent. Higher prices and stricter water-pollution laws have prodded industries to recycle water. The four largest industrial water users – paper, petroleum, chemicals, and primary metals – have all cut back, by using processes that require less water and by using the same water several times.

More than 36 billion gallons of water each day feeds industrial demand. Of that, mines use about three billion gallons; 8.3 billion gallons supplies commercial users, including military bases, college campuses, office buildings, and restaurants.

Domestic.

Across the United States, people are using less water as they take showers, flush toilets, and water lawns. After climbing between 1960 and 1985, per capita domestic water use has declined slightly. Water conservation campaigns and new building codes are behind the change. First viewed as a state and local matter, domestic water conservation has evolved into a national issue: Federal law now requires manufacturers to produce only low-flow toilets and showerheads. To cut down on lawn sprinklers and other garden water use, several states now encourage the use of landscaping techniques adapted to the local environment.