I'm reminded of the farmer who was asked whether he believed in baptism. He replied, "Of course. I've seen it done."
Well, as the ethanol boom has continued, I've seen new corn fields in Arizona and California where farmers water the fields with groundwater. Foolishness, oft repeated, does not become wisdom. Repeated claims by some of the comments that little corn is irrigated must come to terms with the map of the Renewable Fuels Association of the location of ethanol refineries in the US. Many are in the arid West.
For those interested in how much water it takes to grow corn, the Water Eduation Foundation (a respected California NGO) thinks it's 2,500 gallons of water to grow enough corn for 1 gallon of ethanol. The respected environmental writer, Ted Williams, pegs the figure at 1,700 gallons.
One comment gives a link to an article from Southwest Hydrology, but that article concedes that groundwater is often the water used for ethanol refineries.
Two larger points. First, I don't mean to pick on ethanol unfairly but it does use lots of water. So does almost every other type of energy production, including for you greenies, concentrated solar thermal. The point I'm making is the intimate connection between energy and water.
Second, the 100th Meridian traditionally marked the boundary between dry land and irrigated farming. But that is no longer true as farmer in the midwest, east, and south are increasingly irrigating their fields. This change in agricultural practices poses a substantial challenge as many parts of the country contront water shortages.