Quiz: What You Don't Know About Water and Energy

Water "consumed," or lost to evaporation, would be about 3 million gallons (11.3 million liters). Water withdrawn from rivers, lakes and other sources would be substantially more, 300 million gallons (1.1 billion liters) per day in plants with so-called "once-through" cooling systems. But most of that water is discharged back to its source, at a higher temperature, after it circulates through the plant cooling cycle.

Coal, nuclear, and other power plants that need cooling water for steam-driven turbine generators are responsible for about 40 percent of freshwater withdrawals, making thermoelectric generation the largest freshwater use in the United States. Agricultural irrigation is a close second, at 37 percent.

Nuclear power plants with cooling tower systems typically consume 720 gallons (2,725 liters) per megawatt-hour due to evaporation, compared to 400 gallons (1,514 liters) for once-through cooling, according to the U.S. Electric Power Research Institute.

Some new designs of combined-cycle natural gas power plants use air-cooled condensers for their steam cycles, creating plants that use virtually no cooling water.

The process that has unlocked vast quantities of natural gas from shale formations in the United States in the past decade, "fracking," involves injecting 2 million to 5 million gallons (7 to 19 million liters) of water at high pressure to create small fractures in the rock, causing the gas to be released.

Some 2.8 to 6.6 gallons (10.6 to 25 liters) are needed to produce each gallon of crude oil from conventional wells in Saudi Arabia or the United States and refine it into motor fuel. Water is produced from wells along with crude; recycling it can cut freshwater use. Unconventional production, accounting for an increasing share of global oil production, often requires more water.

About 780 gallons, according to a U.S. National Research Council report, derived from recent figures showing irrigation for Nebraska corn at 2,100 gallons (7,949 liters) of water per bushel and each bushel yielding 2.7 gallons (10.2 liters) of ethanol.

Paper manufacturer H.J. Rogers spearheaded construction of the world’s first hydroelectric power plant, which began operation on the Fox River in Appleton, Wisconsin, in 1882. It generated enough electricity to power his house, the plant itself, and a nearby building.

Norway gets 99 percent of its electricity from hydropower, and Albania is close behind at 98 percent. Iceland gets 75 percent of its power from hydro; in France, the share is 10 percent.

Electricity is used for water pumping, conveyance, treatment, and distribution, making it the largest single cost of public water systems.