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23 April 2008—Remember when you were a kid and your parents made a big fuss about turning off the light when you left a room? Who knew that, besides adding to the monthly electric bill, keeping a single 60-watt lightbulb lit for 12 hours uses as much as 60 liters of water? According to researchers at the Virginia Water Resources Research Center, in Blacksburg, Va., fossil-fuel-fired thermoelectric power plants consume more than 500 billion L of fresh water per day in the United States alone.

“That translates to an average of 95 L of water to produce 1 kilowatt-hour of electricity,” says Tamim Younos, associate director of the center and a professor of water resources at Virginia Tech, where the center is housed.

Why so much? Water plays a number of roles in energy production, including pumping crude oil out of the ground, helping to remove pollutants from power plant exhaust, generating steam that turns turbines, flushing away residue after fossil fuels are burned, and keeping power plants cool.

Younos and his colleagues have combed through dozens of government and academic research papers in order to tease out just how much water is consumed during the production of a dozen types of fuel. “The basic information is generally available from scientific literature and governmental documents. However, these documents do not express water use for various technologies in a consistent unit,” says Younos. The team, after gathering the numbers from disparate sources, converted them to gallons of water per million Btu of energy. IEEE Spectrum converted their findings to L/1000 kWh, or the amount of energy required to power 1000 homes in the United States for one day.

What the Virginia Water Resources group found is both heartening and distressing. Natural gas, the fuel of choice for most of the ultraefficient electricity-generating turbines being built to meet the world’s growing energy demands, yields the most energy per unit volume of water consumed. Fewer than 38 L of water are required to extract enough natural gas to generate 1000 kWh of electricity. By the time a coal-fired power plant has delivered that much energy, roughly 530 L of water has been consumed.

The big shocker is that biodiesel doesn’t look so “green” when considered in the context of water consumption. More than 180 000 L of water would be needed to produce enough soybean-based biodiesel to keep the lights on for one day in 1000 homes. Younos explains that it takes a lot of water to irrigate the soil in which the soybeans grow, and even more is used in turning the legumes into fuel.

Here are the Virginia Water Resources Research Center results by fuel source:

The researchers also looked at water consumption by type of electricity generation:

source :  http://spectrum.ieee.org/apr08/6182