“We are not very mature on this type of cross-sector analysis,” Mr. Granit said.

The water needs of power plants are actually greater than the raw consumption numbers suggest. According to Mr. Hightower, more than 50 percent of the water withdrawn every day from rivers and lakes in the United States goes toward energy production.

Power plants discharge almost all of that water back into rivers or ponds after it has helped cool the plant (which explains the difference between 4 percent consumption and 50 percent withdrawals).

However, this means that in times of drought, when rivers or reservoirs are drying up, power plants may have trouble finding enough water, even if they end up discharging most of it.

“You don’t just pick these things up and move them,” Mr. Hightower said, referring to power plants.

The water the plants discharge is also warmer and can affect the environment downstream, Mr. Hightower said.

The water-saving technologies in power plants are improving, and there is a trend toward cooling systems in which more water is recycled, said Mr. Larsen of DHI. The potential for improvements is large: A recent paper by University of Texas academics in the journal Environmental Research Letters reports that changing the cooling technologies used by power plants in 11 Texas river basins could reduce the water they divert each year by an amount equivalent to the annual water use of at least 1.3 million people.

Hydroelectric facilities — which account for about 16 percent of global electricity production — are also vulnerable to drought, of course.

Power plants are not the only reason energy production depends on water. Extracting oil and natural gas from the ground with hydraulic fracturing techniques requires prodigious amounts of water.