The federal standards for acceptable levels of pharmaceutical residue in bottled water are the same as those for tap water - there aren't any.

The Food and Drug Administration, which regulates the $12 billion bottled water industry in the United States, sets limits for chemicals, bacteria and radiation, but doesn't address pharmaceuticals.

Some water that's bottled comes from pristine, often underground rural sources; other brands have a source no more remote than local tap water. Either way, bottlers insist their products are safe, and say they generally clean the water with advanced treatments, though not explicitly for pharmaceuticals.

Nestle Waters North America Inc., an industry leader whose brands include Arrowhead, Poland Springs and Ozarka, said it selects sources that are removed from human activity, increasing the chances that the water will be pure. It then runs the water through three cleansing stages.

"We know that our multiple barrier process is effective," said Kevin Mathews, the company's director of health and environmental affairs.

Absent a regulatory mandate, however, Nestle follows the industry norm and does not test for pharmaceuticals. And given that testing can detect extremely small concentrations, Mathews would not rule out the presence of traces of pharmaceuticals in its water.

"I don't think anybody could say anything is free" from pharmaceuticals, Mathews said.

Annual bottled water consumption in the United States has increased about 50 percent, to 30 gallons per person, according to the Beverage Marketing Corporation.

"The industry is monitoring it," said Bob Hirst, a vice president at the International Bottled Water Association, which represents dozens of brands. "But we haven't seen anything to alarm us at this point."