It is easy to overlook that most of the energy we consume daily, such as electricity or natural gas, is produced with the help of a dwindling resource – fresh water. Virginia Tech professor Tamim Younos and undergraduate student Rachelle Hill are researching the water-efficiency of some of the most common energy sources and power-gen-erating methods.

The researchers have analyzed 11 types of energy sources (biodiesel, coal, fuel ethanol, liquefied natural gas, synfuel-Fis-cher Tropsch, tar sands, oil shale, hydrogen, synfuel-coal gasification, petro-leum/oil and nat-

ural gas) and five power-generating methods (hydroelectric, fossil fuel thermoelectric, nuclear, solar thermoelectric and geothermal).

Younos says they based their calculations on available gov- ernmental reports by using a standard measurement unit, which makes this study unique. “Our unit is gallons of water per British Thermal Unit (BTU),” explains Younos. “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.”

According to the study, the most water-efficient energy sources are natural gas and synthetic fuels produced by coal gasification. The least water-efficient energy sources are fuel ethanol and biodiesel. In terms of power generation, Younos and Hill have found that geothermal and hydroelectric energy use the least amount of water, while nuclear plants use the most.

Hill took the study one step further and calculated how many gallons of water are required to burn one 60-watt incandescent light bulb for 12 hours a day, over the course of one year. She found that the bulb consumes between 3,000 gallons and 6,000 gallons of water, depending on how water-efficient the power plant that supplies the electricity is. Hill adds that the results are estimates of the water consumption based on energy produced by fossil fuel thermoelectric plants, which produce most of the U. S. power (53.1%). “The numbers are even more staggering if you multiply the water consumed by the same light bulb by the approximately 111 million U.S. homes,” says Hill. “The water usage then gets as high as 655 billion gallons of water a year.” By contrast, burning a compact fluorescent bulb for the same amount of time would save about 2,000 gallons to 4,000 gallons of water per bulb, per year.

Younos notes that the results of this analysis should be interpreted with a grain of salt. “There are several variables such as geography and climate, technology type and efficiency, and accuracy of measurements that come into play. However, by standardizing the measurement unit, we have been able to obtain a unique snapshot of the water used to produce different kinds of energy.”