The Intertwined Tale of Energy and Water

Energy production requires a large amount of water. Which technologies are the most water-efficient, and which are the least?
August/September 2008
http://www.motherearthnews.com/nature-and-environment/water-as-energy-source.aspx
As electricity demand rises, so does the demand for water. Read on to find out how much water is used by various energy production technologies...


ISTOCKPHOTO/DAVID JOYNER

Ecologist Jacques Cousteau once said, “Sometimes we forget that the water cycle and the life cycle are the same.” What he meant was that not only human survival, but all life on Earth, totally depends upon water.

Our modern world is also driven by energy use — we need energy for producing food and clean water; for providing electricity in our homes, businesses and industries; and for transportation.

But did you know that energy production depends on water? Conventional production of energy and power requires a huge amount of water. Power plants require water to scrub pollutants (generated from burning coal, for example), to produce the steam necessary to turn huge turbines and generators, and more. Even some alternative energy sources, such as ethanol and hydrogen, require large volumes of water. As electricity demand rises, perhaps as much as 50 percent in the next 25 years, the demand for water also will increase.

Crunching Numbers

So how much water is used by various energy production technologies? To illustrate the water use for various technologies in a consistent unit, the chart at right shows water usage in gallons of water used per British thermal unit (Btu), which indicates pure energy as heat. Btu is applicable to all energy production and power generation methods.

The chart shows that in terms of fuel production, soy-based biodiesel is the least water-efficient energy source, followed by corn-based ethanol. Natural gas is the most efficient. In terms of electricity generation, nuclear energy is the least efficient while hydroelectric power is the most efficient system.

Consider the example of the common incandescent light bulb: If we assume that a household will burn a single 60-watt light bulb for 12 hours, it adds up to 0.72 kilowatt hours (kWh). If this light bulb is powered by electricity from a fossil-fueled plant (as is the case for most of the power produced in the United States), that converts to 10,022 Btus per kWh. (The conversion rate of kWh to Btus depends on the efficiency, or heat rate, of the various fuel sources or power generation methods.)

Hence, a single light bulb will consume about 7,200 Btus in one day. From the chart, it can be estimated that fossil fuel thermoelectric plants use between 1,100 to 2,200 gallons of water per million Btu to generate power. This equates to approximately 8 to 16 gallons of water used to make the power needed to run one 60-watt light bulb for 12 hours! Over the duration of one year, this one incandescent light bulb would require about 3,000 to 6,300 gallons of water. Furthermore, it is estimated there are about 111 million occupied housing units in the United States. If each housing unit burned only one light bulb for 12 hours a day, over the course of a year it would add up to about 300 to 650 billion gallons of water.

Think About it

In the near future, increased energy development will compete for available water resources with other water demands, such as agricultural irrigation and domestic water supplies. As the chart shows, some new initiatives, such as biodiesel and ethanol production, require very large amounts of water. Future production and the cost of energy will be impacted by water availability. There is an urgent need to consider water availability in proposed energy policies.


Reprinted with permission from Virginia Tech.