E85 Boondoggle of the Day: 2100 Gallons of Water Per Gallon of E85?

David C. Holzman
by David C. Holzman

Corn-based ethanol took another blow from the scientific literature this week. University of Minnesota scientists published an article revealing that corn into E85 could require three times as much water as previously estimated. The bottom line: it takes more than 2,100 gallons of water to produce a single gallon of ethanol. That’s bad news for corn-etoh’s partisans; water supplies in the US are not exactly ample (as the NYT Mag pointed out a couple of years ago in its article, “ The Future Is Drying Up“). Ethanol has also been bashed for competing with food, and for raising carbon emissions over a period of decades, rather than reducing them. The researchers, led by Sangwon Suh, note that the water needs vary widely depending on irrigation practices. In a dozen Corn Belt states, production of a gallon of E85 requires less than 100 gallons of water. I still wouldn’t buy any stock . . .


In general, land plants require huge amounts of water—so much so that Harvard University forestry professor Michele Holbrook considers growing on land one of the six “impossible tasks” that plants do. The problem is that pulling carbon dioxide—which becomes the structural material of plants—is like sifting needles from haystacks. CO2 makes up 3.8/100ths of a percent of the stuff we breathe in, while the concentration is considerably higher in water.

Thus, the plant needs to ingest huge quantities of air vial the leaves, but the extensive surfaces for absorbing the air lose water fast. Thus, about 500 water molecules must cycle through the plant for every carbon dioxide molecule the plant captures. “If I turned the mass of my body into sunflower leaves, I’d have to drink two liters every 30 seconds,” says Holbrook.

Holbrook recently added a 7th task to her list of impossible tasks of plants: sustainably producing liquid fuels from crops. There’ll be no joy in Mudville over this one . . .

David C. Holzman
David C. Holzman

I'm a freelance journalist covering science, medicine, and automobiles.

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  • David C. Holzman David C. Holzman on Aug 07, 2009

    Sugar cane is a much more productive crop for ethanol than corn, but if you believe global heating is a problem--and I know many ttac readers don't, but please lets not get into another argument about THAT--the US tariff is preventing a lot of carbon emissions that would happen if the brazilians increased production of sugar cane. To understand that, you can click on the link I provided in the blog about the carbon impact of biofuels. But ohsnapback is absolutely right about the reason for the tariff. Twotone may well be right about algae farms. The carbon impact link covers that as well. (I wrote it.)

  • Ohsnapback Ohsnapback on Aug 07, 2009

    David Holzman - Thanks for that link; interesting stuff.

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