Asbestos, bacteria, bromates, chlorine and its byproducts, fungicides, heavy metals (including lead and mercury), industrial solvents, nitrates and nitrites, parasites, pesticides, pharmaceutical drugs, plastics, radium, uranium, and viruses: All of these unwanted substances—and more—show up in U.S. drinking water. A recent Environmental Working Group report on tap water in 42 states found that more than 16 million Americans had been drinking chlorinated byproducts for 12 consecutive months. In some cases, contaminant levels were five times higher than the maximum allowable limits.

Who’s Checking?

The Environmental Protection Agency (EPA) regulates a number of these contaminants in tap water under the National Primary Drinking Water Standards. Unfortunately, maximum allowable contamination levels have been established for only about 80 toxins. Compliance with Secondary Drinking Water Standards, established in 1992 to help protect tap water safety, is only voluntary. Plus the EPA’s position on a number of substances—including aluminum and fluoride—remains open to question, despite research showing health risks to certain individuals from both.

The U.S. Geological Survey routinely monitors surface and groundwater for arsenic, bacteria, pesticides, radionucleotides, and volatile organic compounds. In addition, state officials, municipalities, and private water companies can test and regulate drinking water in this country.

The U.S. Food and Drug Administration (FDA) monitors bottled water, which is considered a food product (go figure). Trouble is, bottled water does not have to be 100 percent free of all contaminants, although any that are present must be below maximum levels permitted by the FDA or the state. Nor are bottling plants required by law to disclose their sources. Aquafina, for example, draws on municipal water in Detroit and Fresno. The Natural Resources Defense Council reports that 40 percent of bottled water is simply treated tap water.

What’s a Consumer to Do?

While smell and taste offer some minimal guidance as to water safety, too many contaminants go undetected. Whether it comes from a municipal plant or a well, have your water tested periodically. Home plumbing problems can impact water quality, so run tap water for 20 seconds to clear out any chemicals leached from pipes overnight. For information on your tap or well water, contact your local health department or the EPA Safe Drinking Water Hotline, www.epa.gov/safewater, or call 800-426-4791.

Look for bottled or mineral water that states its origin and contents. Independent organizations like NSF International test bottled water—unannounced—for compliance with federal guidelines and for more than 160 contaminants. (This certification process, however, is voluntary.) It’s wise to store bottled water in a cool place, away from cleaning agents, gasoline, and solvents.

“I urge people to use purified drinking water and to avoid the faucet,” says Elson M. Haas, MD, founder and director of the Preventive Medical Center of Marin. “I personally have not drunk tap water in more than 20 years; instead, I have used well water or spring water collected from mountain or underground sources (unfortunately these waters can be contaminated also) or, more recently, home-filtered tap water using a reverse osmosis (RO) system.” NSF also tests home water treatment systems: Call its Consumer Affairs office at 877-867-3435, or e-mail info@nsf.org.