Now taking its place alongside the notion of a carbon footprint as an issue of major environmental concern is a term you may expect to hear more in the future: a water footprint. The planet has a limited water supply, and as our population grows, that supply is becoming strained. The water footprint is a way of measuring consumption (as opposed to output, in the case of the carbon footprint).

There are obvious and immediate ways people are thinking about their own daily water usage (showers, laundry cycles); a popular Web site, waterfootprint.org allows visitors to calculate their own water footprint, based on their habits, and to learn how much water went into various common foods they eat. Food is one of the large-scale uses of water that’s also gaining more attention. As concern for the water supply grows, agriculture, which accounts for half of the water use in this country, is likely to receive increased scrutiny.

For years, outlandish claims have been floated about the amount of water cattle production re-quires. Producing a pound of beef is said to take anything from 2,500 gallons of water to as much as 6,000 gallons (ac-cording to Stanford professors Paul R. and Anne H. Ehrlich in their book Population, Resources, Environment). Newsweek once reported that the water required by a 1,000 pound steer over its lifetime “would float a destroyer.”

But other researchers have come up with very different figures. Jim Oltjen, in the Department of Animal Science at U.C. Davis, asserts a pound of beef actually requires 441 gallons of water. NCBA uses his research to answer claims of egregious water waste in the beef industry, as they do at length on their Web site, beeffrompasturetoplate.org.

In 1999, the CAST Animal Agriculture and Global Food Supply Report came to almost the same conclusion, after considering all factors in beef cattle production related to water  —  consumption, irrigation and processing  —  saying it took 435 gallons of water to produce a pound of boneless beef.

That still sounds like quite a bit of water, but consider that, according to waterfootprint.org, a pound of rice requires 403 gallons of water and a pound of chocolate needs 2,847 gallons. (Keep in mind this site also lists beef at about 2,000 gallons per pound.)

And while half our water does go to agriculture, of course it’s not the case that all, or even most, of it is going to grow feed for livestock, as some have claimed. Research published in the Journal of Animal Science concluded that our total livestock production took just about 11 percent of our water. The water to grow crops that become livestock feed was 9.7 percent of all water use; livestock consumption, at 1.2 percent of water use, made up the rest of the total.

As for the floating destroyer claim, the NCBA Web site puts that to rest as well. They use the U.S. Navy’s report that a destroyer needs about 2.11 million gallons of water to float. As we’ve learned, it takes 435 gallons of water to create a pound of boneless beef. If a steer weighing 1,000 pounds yields 450 pounds of boneless beef, that means it needs a total of 195,750 gallons of water  —  which would leave the destroyer high and dry.