A high-yielding corn crop requires about 22 inches of water, with a range of 20 to 25 inches. About 15-16 inches of water is enough to produce a low yield, but that depends on when during the season the water is available or unavailable. In general, higher yields need more water but factors like temperature affect this to some extent.
One inch of water per acre is about 27,000 gallons per acre, so a corn crop uses about 22 x 27,000 = 594,000 gallons of water. If the yield is 200 bu, that means that the crop uses almost 3,000 gallons of water for each bushel of yield.
For more information on this or other topics related to corn production, contact your state extension corn specialist or your local extension educator/agent.
The following is the link to the corn extension specialists: state extension corn specialist