Measuring Corn Ethanol's Thirst for Water

Ethanol derived from corn consumes up to three times more water than previously thought, according to a new study.

Prior studies have estimated, based on national production averages, that one liter of corn-derived ethanol should require 263 to 784 liters of water to both grow the crop and convert it into fuel. Now, researchers at the University of Minnesota have concluded that the amount of water used in ethanol production varies hugely from state to state, ranging from 5 to 2,138 liters of water per liter of ethanol, depending on regional irrigation needs.

Corn ethanol is already plagued by environmental concerns such as pollution from fertilizer, pesticides, and herbicides; soil erosion; greenhouse-gas emissions from production; and competition for agricultural land with food crops.

The new study, published in the journal Environmental Science and Technology, also found that as corn-based ethanol production has approximately doubled nationwide between 2005 and 2008, related water use has more than tripled.

“Ethanol consumes more water over time as corn production extends to regions that need extensive irrigation,” says Sangwon Suh, an assistant professor of biosystems engineering at the University of Minnesota and coauthor of the study. “That means more water is needed to produce a given unit of ethanol over time.”

Suh and his colleagues examined state and county records on irrigation use for growing corn, both as food and for fuel, as well as the location, production levels, and water usage of existing corn-ethanol facilities. The researchers found that more than 80 percent of the corn used to make ethanol is harvested within a 64-kilometer radius of the refinery where it is converted into fuel. Using this information and data on local rates of irrigation, the researchers were able to estimate the water requirements of individual corn-ethanol production facilities.

In some states, such as Ohio, Iowa, and Kentucky, where corn can grow with little to no irrigation, only five to seven liters of water are required to turn the foodstuff into fuel. Almost all of this water is used to boil, ferment, and distill the biofuel. As ethanol production has increased, however, more corn is being grown in western states such as Nebraska, Colorado, and California, where irrigation needs raise the fuel’s water requirements significantly.

“This is one more nail in the coffin for ethanol,” says David Pimentel of Cornell University, in Ithaca, NY, whose own studies have shown that ethanol requires more energy to produce than it releases when burned, and that the fertilizer used to grow corn for ethanol has contributed significantly to dead zones in the Gulf of Mexico (areas of the ocean with low oxygen content due to increases in chemicals in the water).

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.