Measuring Corn Ethanol's Thirst for Water

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Water everywhere: Total water requirements for the irrigation and conversion of one liter of ethanol by state, as well as the total water used in ethanol production by state. Credit: Environmental Science and Technology

The U.S. Energy Independence and Security Act of 2007 mandates that ethanol produced using existing technologies will have to increase from the 34 billion liters produced in 2008 to 57 billion liters per year by 2015. This includes the more arid western states, where corn-based ethanol is currently produced.

Jerry Schnoor of the University of Iowa, in Iowa City, says that ethanol producers are already planning additional production facilities in all states to meet the 2015 goals. "We're already in an unsustainable situation in terms of water use, already drawing down aquifers like the Ogallala," Schnoor says of the vast underground water source stretching from South Dakota to northern Texas. "This would exacerbate that decline if we expand in these irrigation states."

Geoff Cooper, vice president of research at the Renewable Fuels Association in Washington D.C., questions the researchers' claim that water use has tripling as ethanol production has doubled. "The bulk of expansion from '05 to '08 occurred in the central corn belt--places that don't irrigate corn," he says. "There is a finite limit to how much ethanol you can put in water-constrained areas. We are not putting ethanol plants into areas where water is severely limited."

Suh is also optimistic that water use can be reduced while ethanol production continues to grow. He says that agricultural land that has been set aside for conservation in regions that do not require irrigation could be brought back into production, and genetically engineered corn could maintain high yields with lower water requirements.

"I'm very optimistic we can achieve the ethanol production mandate without sacrificing water security in the U.S.," he says. Schnoor adds that ethanol production could expand to the south and east, where land is cheaper and water is more plentiful.

Pimentel, however, disagrees. "You read the paper and the conclusion is certainly that it will require more and more water, but [Suh] is from Minnesota, and you have to be cautious because in Minnesota they are promoting ethanol," he says.

The study was funded in part by the Department of Energy and the state of Minnesota.