An ethanol industry group says the report offers little new insight and the vast majority of ethanol is produced from rain-fed corn.
The November study from the Government Accountability Office quotes Argonne National Laboratory data saying that farmers in North Dakota, South Dakota, Nebraska and Kansas use, on average, 323.6 gallons of water to produce one gallon of ethanol from corn, with all but 3 of those gallons used for irrigation.
The GAO said that's 20 to 30 times the amount of water used in the U.S. Department of Agriculture's two other main corn-producing regions, where rainfall is more plentiful.
Region 5, which includes Iowa, Indiana, Illinois, Ohio and Missouri, uses 10 gallons of water for every gallon of ethanol, while the region encompassing Minnesota, Wisconsin and Michigan uses 16.8 gallons of water.
"As demand for water from various sectors increases and places additional stress on already constrained supplies, the effects of expanded biofuel production may need to be considered," the GAO noted in its report.
Geoff Cooper, vice president of research for the Renewable Fuels Association, said it's disingenuous to suggest that increased ethanol production is somehow driving irrigated corn acreage. He quotes a National Renewable Energy Laboratory article that says 96 percent of corn used for ethanol production is not irrigated.
"We've always irrigated about 12 or 13 percent of the corn crop, and we expect that to continue, with or without ethanol production," Cooper said.