Dozens of chemicals, metals, microorganisms, herbicides and pharmaceuticals pour from our faucets.
Columbus routinely tests drinking water for a state-ordered list of compounds at its three water-treatment plants, which produce more than 50 billion gallons for about 1.1 million people every year.

Records show 54 substances detected in Columbus water since 2001. That includes special tests in 2001 and 2005 that detected four antibiotics, caffeine and possible traces of 12 other compounds, including the insect repellent DEET.

If these compounds are in the water, they're at levels so low that the health effects can't be determined, the city says. Though the federal government and the Ohio Environmental Protection Agency impose limits on 91 compounds and organisms, no standards exist for many more.

A 2005 study of water test results performed by the Washington, D.C.-based Environmental Working Group found 141 contaminants for which there are no standards. That study did not include pharmaceuticals and compounds from detergents, cleaners and other consumer products.

"There are 82,000 chemicals registered for use in the United States, 15,000 in large amounts," said Jane Houlihan, the group's vice president of research. "What utilities are required to test for is a small fraction of what's there."

The question is whether people should be concerned. Farm herbicides found in drinking water, for example, were detected at levels below state and federal health limits.

Antibiotics and chemicals detected in drinking water show up at levels far below what would be considered a medical dose. Researchers are examining potential health effects.

Karen Mancl, director of Ohio State University's graduate program in environmental science, said cities have to balance the number of tests they perform against cost and public risk.

"You could spend lots of money on testing your water, but what we want to do is test the water frequently for things that point us in the direction of other things that could be problems," Mancl said.