How much water do we use?

Almost all of the world's water is saltwater: 97.5 percent. The remaining 2.5 percent is freshwater, but two-thirds of this is locked up in glaciers and ice caps. What remains--in aquifers, soil pores, lakes, swamps, rivers, plant life and the atmosphere--is enough to fill the five Great Lakes about 500 times over.

But much of this water, of course, is not accessible for human use. The amount of renewable water--that contained in the land-ocean-atmospheric cycle--fills up the Great Lakes only twice. Still, not all of this is within easy or timely reach. Of what is practically accessible, humans use about 54 percent each year, about the volume of Lake Michigan. This relatively large percentage of freshwater usage is what makes modern civilization possible, and also what makes it so vulnerable to the influence of climate and the actions of humans themselves.

In the United States, freshwater withdrawal is about 1,300 gallons per person per day, about according to the U.S. Geological Survey--about 20 times that of a standard filled-bathtub. This represents about a quarter of the national renewable supply; of this, about 72 percent is returned to the natural system. Between 1900 and 1995, global water withdrawals increased sixfold, more than twice the rate of population growth. The good news is that per capita water use peaked around 1980, a trend that is expected to continue as we learn to use water more efficiently.

On average, each American consumes more than twice the worldwide average, enough to fill the average backyard swimming pool 18 times in a year, or the hockey rink in the Whittemore Center to a depth of nearly three feet.

Every day each person in a typical single-family home uses 74 gallons of water indoors, with 10 gallons of that lost in leaks, according to the American Water Works Association. Per capita water use could be reduced by about 30 percent by installing more efficient water fixtures and regularly checking for leaks.

Beef production accounts for roughly a third of all freshwater withdrawals in the U.S. It takes 15,000 tons of water to produce a ton of grain-fed beef (and up to 100,000 tons, according to some estimates), but only 1,000 tons to produce a ton of grain. Each 16-ounce porterhouse steak took 1,800 gallons to produce. Each calorie of beef takes 1.5 gallons to produce; each calorie of grain takes only about one cup.

See also: Relocating Beijing?

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