Water in the ethanol process
 Cornell University Professor David Pimentel - perhaps ethanol's most passionate critic - is often quoted in the popular press as saying it takes 1,700 gallons of water to produce just one gallon of ethanol. (Source: "Ethanol Fuels Rural Renaissance." Les Christie. March 9, 2007. CNNMoney.com) Of course Pimentel's catchy sound byte is misleading and ridiculous.
It is true that corn requires large amounts of water to grow. A bushel of corn needs about 4,000 gallons of water in a growing season.
But what often goes unreported is that nearly nine out of every 10 acres used to grow corn in the United States are rain-fed
and require no irrigation whatsoever meaning that as much as 96 percent of the corn used for ethanol is not irrigated. (Source: Aden, Andy. "Water Usage for Current and Future Ethanol Production." Southwest Hydrology.)
Besides water doesn't just simply disappear from the atmosphere when it's used, it changes forms, moves, and reallocates based on conditions. So, when it snows or rains it either serves to revitalize lakes and rivers, collects as groundwater or evaporates. |
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In fact, one acre of corn gives off about 4,000 gallons of water per day through evaporation. (Source: "Water Trivia." U.S. Geological Survey.) That means that the U.S. corn crop returns more moisture to the atmosphere than it uses from irrigation or from surface and groundwater sources.
But what about the amount of water used by ethanol plants? It's been reported that the production of one gallon of ethanol requires an average of three gallons of water. "Use" does not mean "loss" in this process, as a portion of the water used in ethanol production is recycled. The remainder of the water used returns to nature through the condensation, infiltration, runoff, evaporation and the precipitation cycle. The little water that's left returns through the process as wet distillers grains used to feed livestock, or is discharged to holding ponds for reuse later.
The ethanol industry is likely to have utilized an average of about 53 million gallons of water per day in 2007. This is based on the assumption that it will produce 6.5 billion gallons of ethanol. That sounds like a lot of water, but it's important to realize that the ethanol industry utilizes only about 1/100th of 1 percent of the country's water.
It is also important to examine the amount of water used to produce gasoline. While estimates on the amount of water required to produce petroleum products vary widely, NREL conservatively assumes up to 90 gallons of water are needed to refine one barrel of oil and 2.5 gallons of water are needed to produce one gallon of gasoline. That means approximately 350 billion gallons of water are used to refine the amount of gasoline American drivers consume annually. It is also important to note the NREL estimate does not include water resources used for exploration and oil recovery.
While the amount of water required to refine a barrel of oil is likely to increase in the future (as petroleum companies will need to go "farther and deeper" into the earth for oil), the amount of water necessary to produce a barrel of ethanol is certain to decrease.
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In fact, complete recycling of water in the ethanol process has not yet
been achieved, but in the future it seems certain.
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