“THERE'S TOO much attention on water usage by ethanol plants,” says Sangwon Suh, Bioproducts and Biosystems Engineering, University of Minnesota.

As production technology has advanced and ethanol plants have improved water recycling efforts, it takes an average of less than 4 gal. of water to produce 1 gal. of ethanol. This is down from about 10 gal. of water/1 gal. of ethanol produced a decade ago. Depending on where conventional oil is sourced and the type of recovery method used, it can take from 3 to 5 gal. of water to produce 1 gal. of gasoline. Each gallon of gasoline recovered from oil sands can consume up to 8 gal. of water. — Lynn Grooms

The water issue takes on greater significance in areas where crops are irrigated. Suh calculates that when both ethanol process water and irrigation are taken into account, it takes 142 gal. of water to produce 1 gal. of ethanol. A study conducted by Suh and colleagues at the University of Minnesota highlights the need to promote ethanol development in states with lower irrigation rates. The study, “Water Embodied in Bioethanol in the United States,” was published in the March 10 issue of Environmental Science & Technology (pubs.acs.org/doi/full/10.1021/es8031067).

Because irrigation may be used on crops destined for feed grain or other products, it is impossible to assign the precise amount of water consumed only to ethanol. Improved irrigation water management is critical in areas where water is scarce. — Lynn Grooms