The Christian Science Monitor published a story today about water consumption and made some remarks about ethanol and biodiesel which aren't true.
Not surprisingly, while gasoline consumes water at 0.15 gallons per mile, biofuels like ethanol slurp an average of 28 gallons per mile. Biodiesel from soybeans comes in at 8 gallons per mile. Electric cars and plug-in hybrids compare favorably with conventional fossil fuels, consuming a bit more than 0.2 gallons of water per mile. The most watertight combo: electric vehicles recharged through renewable sources of electricity. The study appeared in the Nov. 1 issue of Environmental Science and Technology.
As the quote notes, their information is taken from a recent study. The study looked at irrigated and non-irrigated biofuels. The numbers they quote are for irrigated biofuels.
If ethanol is processed from corn grain in irrigated fields, then water consumption is 1.3−62 gal H2O/mile (average of 28 gal H2O/mile) and withdrawal is 6.9−110 gal H2O/mile (average of 36 gal H2O/mile). Ethanol processed from corn grain from nonirrigated fields results in water consumption and withdrawal intensities of 0.15−0.35 gal H2O/mile and 0.33−0.56 gal H2O/mile, respectively.
Their quoted amount of water consumption for biodiesel is also the number for soy from irrigated fields.
Biodiesel derived from irrigated soybean fields has water consumption of 0.6−24 gal H2O/mile (average of 8 gal H2O/mile) and withdrawal of 1.1−26 gal H2O/mile (average of 10 gal H2O/mile). If the soy fields are not irrigated, then just as with ethanol, the consumption and withdrawal are 2 orders of magnitude less at 0.01−0.02 gal H2O/mile and 0.03−0.12 gal H2O/mile, respectively.
The problem with using the irrigated number is that less than 15% of all corn grown in this country is irrigated. So while a small percentage of the ethanol produced in this country may indeed consume the amount of water they say, the vast majority uses a much smaller amount.
I don't have any numbers on how much of the soy crop is irrigated but I think it is safe to say that not all of it is so assigning the higher irrigated number to all biodiesel would also be less than truthful.
I would have expected better from this organization.
Source : Water Intensity of Transportation