Water usage for ethanol production varies dramatically depending on the state, according to a new University of Minnesota study.

The study, published in this week’s edition of the journal Environmental Science and Technology, is the first to compare water use in corn-ethanol production on a state-by-state basis. The authors used agricultural and geologic data from 2006-2008 to develop a ratio showing how much irrigated water was used to grow and harvest the corn and to process it at ethanol plants.

Among the major ethanol-producing states, Iowa uses the least water, with about six gallons of water used for each gallon of ethanol. On the other end of the spectrum, California – which produces only a tiny fraction of the nation’s ethanol but irrigates most of its corn – uses about 2,100 gallons of water per gallon of ethanol.

The study “highlights the need to strategically promote ethanol development in states with lower irrigation rates and less groundwater use,” the authors say. The study was funded in part by the U.S. Department of Energy and by the Legislative Citizens Commission on Minnesota Resources.