According to REPORT presented at an American Society of Mechanical Engineers conference in 2007 offers some alarming estimates: Producing a gallon (3.79 liters) of corn ethanol, for example, consumes 170 gallons (644 liters) of water in total, from irrigation to final processing. Soybean biodiesel manufacture needs some 900 gallons of water (3,400 liters) per gallon of fuel. On the other hand, the water requirement to make a gallon of regular gasoline is just five gallons (19 liters).

Checkout the report for more interesting analysis.

I try not to buy ethonal for my truck as I see a reduced mileage from it. It is a f150.