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January 13, 2010

Water consumption questions for biofuels—irrigated or non?

It is well accepted that consumptive water use in ethanol distilleries ranges from 3 to 4 gallons of water per gallon of ethanol, but this is only part of the story. Water consumptive use for crop growth differs by climate regime and  must be differentiated between rain-fed agriculture—where irrigation, if used at all, may supplement rainfall only during periods of extreme drought—and irrigated agriculture, as practiced west of the 100th meridian (essentially west of the Missouri River for the northern states).

If one calculates ethanol water use on a “gallons per mile” basis (a hard term to use because it depends on assumptions and vehicle fuel efficiency) the values are startling—up to 62 gallons of water are used per mile driven if irrigated corn is used for ethanol production. 

U.S. Department of Interior Secretary Dick Kempthorne, quoted in a recent issue of Ethanol Producer Magazine stated: “To reach our ethanol production target of 7.5 billion gallons per year by 2012 will require 30 billion gallons of water a year to process, or the amount of the annual water needs of Minneapolis, Minn. And if just 25 percent of the new corn crop requires irrigation, ethanol will demand more water than the combined annual usage of all cities in Arizona, Colorado, Idaho and Nevada. As we increase ethanol production, we must have a holistic approach that takes into account its impact on water supply.”

Yet, we are now slated for over 12 billion gallons of ethanol per year by 2012 and the U.S. already has a total capacity, as of September 2009, of over 13 billion gallons per year, which according to the Renewable Fuel Standard, is set to grow quickly to 36 billion gallons per year by 2022.

While ethanol from cellulosic sources is slated to overtake ethanol from corn, the difficulties of developing commercial-scale cellulosic ethanol plants are considerable. And there is no indication that cellulosic crops will actually lower water use. What is of concern is that the increasing push for ethanol from corn will result in corn production stretching beyond the usual rain-fed agricultural regions, where more of the land must be irrigated. For example over 80 percent of the corn land in Nebraska is currently irrigated and there are calls for increased land for irrigated corn production.

The title of a November 2009 GAO report stated it well: “Many Uncertainties Remain about National and Regional Effects of Increased Biofuel Production on Water Resources.” These uncertainties need to be better understood to ensure that biofuel production does not put our water resources at risk.

Dennis Keeney

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