'New' Energy Sources Hard on Water Supply

April 23, 2008 — -- Guess how much water it takes to burn just one 60-watt incandescent light bulb 12 hours a day for one year. Between 3,000 and 6,000 gallons of water — depending on how the electricity that powers the bulb is produced.

That's just one in a whole bunch of startling findings in a study by researchers at Virginia Tech who focused on a problem that has probably eluded most folks. It takes lots of water to produce energy, and rising energy demands will almost certainly tap into a rapidly dwindling supply of fresh water.

Some of the thirstiest energy sources are the same ones that are now getting the strongest push, such as ethanol and biodiesel.

"Basically, all the conventional energy sources are water dependent," research professor of water resources Tamin Younos said in a telephone interview.

That won't come as a surprise to scientists at the federal departments of agriculture and energy, who have produced numerous reports tallying up the enormous quantities of water used to produce fuel and electricity. But Younos and an undergraduate assistant, Rachelle Hill, took those same reports and added a new twist.

Younos wanted to determine the water-use efficiency of various energy sources, but that's not easy because energy comes in so many different packages, from watts to joules and so forth. The researchers needed some unit of measurement that all energy sources have in common. So they came up with the British thermal unit (BTU).

"We selected BTU as a standard unit because it indicates pure energy as heat and is applicable to all energy production and power generation methods," Younos said. A BTU is the amount of energy required to raise the temperature of one pound of water from 58.5 degrees Fahrenheit to 59.5 degrees.

The researchers looked at 11 different fuels used to produce energy, ranging from natural gas (a frugal water user) to biodiesel (a real water pig), and five different types of power plants, from hydroelectric (frugal) to nuclear (a pig, but some plants use water from the ocean, not fresh water.)