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.

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."