Okay, I found an article about the water used per gallon of Ethanol.
MinnPost - University report warns water consumption for corn-ethanol on the rise
The rate for Minnesota Ethanol plants is 3.5:1 water:Ethanol. Which is good for their unirrigated land. The irrigated land raises the water consumption to 9 gallons of water per gallon of Ethanol
for the state.
These plants produce millions of gallons of Ethanol per year so large amounts of water are used.