28-05-08 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. American researchers have been investigating the water-efficiency of some of the most common energy sources and power generating methods and have come up with some thought-provoking results.
Professor Tamim Younos of the Virginia Water Resources Research Centre based at Virginia Tech and undergraduate student Rachelle Hill analyzed 11 types of energy sources (biodiesel, coal, fuel ethanol, liquefied natural gas, synfuel-Fischer Tropsch, tar sands, oil shale, hydrogen, synfuel-coal gasification, petroleum/oil, and natural gas) and five power generating methods (hydroelectric, fossil fuel thermoelectric, nuclear, solar thermoelectric, and geothermal).

Younos said they based their calculations on available governmental reports by using a standard measurement unit, which makes this study unique.
“Our unit is gallons of water per British thermal unit (Btu),” explained 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 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 and 6,000 gallons of water, depending on the water-efficiency of the power plant that supplies the electricity.
Multiply the water "consumed" by one light bulb by the approximately 111 mm homes in the US and water usage reaches a massive 655 bn gallons of water a year. By contrast, burning a compact fluorescent bulb for the same amount of time would save about 2,000 to 4,000 gallons of water per bulb, per year.

The study is part of a multi-college partnership at Virginia Tech led by Younos that proposes a unique approach to managing water and energy resources, called the Decentralized Energy and Water Systems (DEWS).
Another research theme under the scrutiny by the DEWS scientists is to study rainwater harvesting as an alternative to using water from the public system for non-potable uses and the impact of rainwater harvesting on water and energy conservation and storm water management.