You write in a response to the posed question:
No, where will the water come from, for all that corn???
You wrote: The sky, generally.
The problem the astute writer points out is that about 4 gallons of treated groundwater are used during the production cycle for just a single gallon of ethynol; he is not talking about the water needed for just growing the crops.
In Minnesota plants have been built before anybody realized the plant would use up the greater part of the available ground water supply; in addition to having to deal with this massive amount of contaminated water that has to be cleaned before it can be allowed to enter the water chain again.