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.)
The numbers they came up with should not be etched in stone, because there are many variables that affect the use of water, but all sources use some. Even oil fields use some water to pump back into the ground to maintain down-hole pressure. Power plants use various fuels to produce heat to convert water into steam to turn a turbine and produce electricity. And the new rage, renewal resources like ethanol and biodiesel, use water to grow crops and convert waste into fuel.
In the United States, power plants consume 136 billion gallons of water a day, the researchers found, but they did not distinguish between fresh water and ocean water. Nearly all inland plants, however, rely on fresh water.
The findings also show a wide range in efficiency for nearly all resources because of different ways that the resources are produced. Coal, for example, ranges from a low of 41 gallons of water to a high of 164 gallons to produce a million British thermal units.
But the real bad actors among fuel sources are ethanol, ranging from 2,510 to 29,100 gallons to produce a million units, and biodiesel, ranging from 14,000 to a whopping 75,000 gallons.
The move toward renewable resources, like ethanol, troubles Younos, who is also the associate director of the Virginia Water Resources Research Center based at Virginia Tech.
"Ethanol from corn is not a good way to go for many reasons," he said. "Water is just one reason." Other researchers have found that ethanol production removes vast amounts of acreage from food production, and it is one of the reasons the price of food is rising so rapidly. It is a huge problem in Brazil, where forested regions are being converted to cornfields, thus releasing more greenhouse gases into the atmosphere.
However, there are other sources of ethanol, like switch grass, which would require much less water than corn, Younos said.
But let's go back to that 60-watt light bulb, because it puts the researchers' findings in perspective.
If the bulb is lighted by a fossil-fueled power plant (coal, natural gas, oil) it will require 8 to 16 gallons of water to keep it lit for one 12-hour day. Based on an estimated 111 million occupied housing units in the U.S., if everybody kept one bulb on 12 hours a day for a full year, the amount of water used would add up to 336 to 656 billion gallons of water.
That's just for one light bulb, in each home, for one year. If we knew the total number of light bulbs across the country, the amount of water used would be staggering, or perhaps drowning.
But here's the good news. According to Rachelle Hill, Younos's collaborator, if just one incandescent bulb is switched to a compact fluorescent bulb, it will save 2,000 to 4,000 gallons a year.
If the numbers compiled by Younos and Hill are anywhere near accurate, growing energy demands will place huge demands on fresh water supplies, which are already stretched to the limit in many areas of the world, even the United States. It's a double whammy in the Southwest, where a prolonged drought has robbed a desert region of vast amounts of water at a time of explosive growth in population.
That's a conflict that could someday make the current energy crisis seem like the "good old days."
Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.