It's rough enough that the millions of Americans who buy bottled water are paying for something that used to basically be free. But even harder to stomach is the message that comes on the bottle: Like milk and eggs, water now "expires."

Most commercially produced water comes stamped with expiration dates -- typically within two years of when it was bottled. On most Poland Spring bottles there are tiny, white letters advising consumers to drink up within two years. Most Aquafina bottles sport two-year expiration warnings on their caps. In general, the dates on bottled water include the prefix "EXP," meaning "expires." Fiji brand water has a slightly different approach: Its bottles say "Best by" followed by the date. Coca-Cola Inc. puts a one-year expiration date on its Dasani brand water.

The message that water has a shelf life has been further amplified in the wake of Sept. 11. The U.S. Department of Homeland Security urges people to stockpile water in their disaster-preparedness kits. On its Web site (www.ready.gov), it instructs people to change their stored water every six months.

The American Red Cross also advises people via its Web site to replace their stored water every six months. But when contacted, the organization's manager of disaster education, Rocky Lopes, says people should replace their bottled water before its expiration date. "The water should be replaced if the manufacturer determines there is a reason for it," he says.

But does water really spoil? Despite the labels reminding consumers to drink up, there is virtually no evidence that drinking water beyond the expiration date has any health impact at all. The Food and Drug Administration considers bottled water to have an "indefinite shelf life." Even the bottled-water industry is hard-pressed to justify the labels.