There has been much controversy regarding the amount of water used to produce a gallon of ethanol. Considering just the usage in the ethanol plant (ignoring any irrigation requirements for the corn), this amounts to about 4 gallons of water per gallon of ethanol produced:
Generally, an ethanol plant will use 10 gallons of water per minute for each 1 million gallons of ethanol produced. A typical 50 million gallon plant, would need 500 gallons per minute of water.
There are no publicly available records on water use by ethanol plants in the United States, the authors found, with the exception of the Minnesota Department of Natural Resources.
Minnesota plants use a range of 3.5 to 6 gallons of water per gallon of ethanol. Average water use has declined from 5.8:1 in 1998 to 4.2:1 in 2005.
Authors of the paper said 4 gallons of water per gallon of ethanol is a good estimate with the current technology.
I have frequently been asked how this compares to the water usage for an oil refinery, and each time I do some back of the envelope calculations and come up with about 0.5 gallons of water per gallon of crude oil processed. But the question comes up often enough that it is worth documenting.
According to an article in the February 18, 2007 Billings Gazette:
Here are the top users of the Billings Public Utilities Department
TOP WATER USERS (GALLONS PER YEAR)
1. Billings Heights Water District, 848 million.
2. ConocoPhillips Refinery, 456 million.
3. PPL Montana, 53.4 million.
4. Casa Village Mobile Home Court, 49.6 million.
5. St. Vincent Healthcare, 39.6 million.
The ConocoPhillips refinery in Billings processes 62,000 bbls of crude oil, or 2.6 million gallons per day. The reliability of most refineries is in the 90-95% range, so if we assumed 92.5% on-stream time, the refinery processes 2.6 million * 365 * 0.925, or 879 million gallons of crude oil per year. The water usage then amounts to 456 million/879 million, or 0.52 gallons of water per gallon of crude oil processed.
Note that this is actual make-up water that is brought into the refinery. In other words, this is the actual usage of the refinery.