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Ethanol's green goodness clouded by water strains

Bob Tippee

For a supposedly clean-burning gasoline additive, ethanol always has carried a full load of environmental compromises.

The problem of volatility is a longstanding example. It’s why ethanol promoters focus on tailpipe emissions of ozone precursors and ignore evaporative emissions. Generally, ethanol improves the former but aggravates the latter.

And it turns out that ethanol from corn—most of the ethanol burned as fuel in the US—doesn’t live up to its press notices as a way to combat global warming. To sweep this one under the rug, ethanol promoters want everyone to ignore the forests displaced by fuel-crop agriculture.

New to the list of questions about ethanol’s environmental goodness is water use.

Growing mandates for the fuel additive through 2022 require energy conservation and careful planning for land use and crop choices, warns a new study published by the Shell Center for Sustainability at Rice University in Houston.

The water needed to grow feedstock for a liter of ethanol in the US ranges from 500 l. to 5,000 l., the study says, depending on crop and location.

For ethanol from irrigated corn grown in Nebraska, travel in a car that achieves 16 mpg of ethanol represents the use of about 50 gal of water/mile driven (gwpm), the study calculates.

“This value could decrease to 23 gwpm for corn grown in Iowa or increase to 90 gwpm if sorghum ethanol is used or to 115 gwpm if the sorghum is grown in Texas,” it says.

The peak mandate for corn ethanol in 2015 could require 6 billion cu m/year of water for ethanol, about 3% of the total used for US irrigation in 2000, the study estimates.

The ethanol mandate also will hurt water quality by raising the use of nitrogen fertilizer and pesticides, it adds.

“Such threats to water availability and water quality at local to national scales represent a major obstacle for sustainable biofuel production and require careful assessment of crop selection and management options,” the study says.

That kind of planning has been ostentatiously absent in the agricultural gold rush incited by US subsidies and mandates for ethanol.

(Online June 12, 2009; author’s e-mail:

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