Millions Drink Tap Water That Is Legal, but Maybe Not Healthy The 35-year-old federal law regulating tap water is so out of date that the water Americans drink can pose what scientists say are serious health risks - and still be legal. Skip to next paragraph Only 91 contaminants are regulated by the Safe Drinking Water Act, yet more than 60,000 chemicals are used within the United States, according to Environmental Protection Agency estimates. Government and independent scientists have scrutinized thousands of those chemicals in recent decades, and identified hundreds associated with a risk of cancer and other diseases at small concentrations in drinking water, according to an analysis of government records by The New York Times. But not one chemical has been added to the list of those regulated by the Safe Drinking Water Act since 2000. Other recent studies have found that even some chemicals regulated by that law pose risks at much smaller concentrations than previously known. However, many of the act's standards for those chemicals have not been updated since the 1980s, and some remain essentially unchanged since the law was passed in 1974. All told, more than 62 million Americans have been exposed since 2004 to drinking water that did not meet at least one commonly used government health guideline intended to help protect people from cancer or serious disease, according to an analysis by The Times of more than 19 million drinking-water test results from the District of Columbia and the 45 states that made data available. In some cases, people have been exposed for years to water that did not meet those guidelines. But because such guidelines were never incorporated into the Safe Drinking Water Act, the vast majority of that water never violated the law. Some officials overseeing local water systems have tried to go above and beyond what is legally required. But they have encountered resistance, sometimes from the very residents they are trying to protect, who say that if their water is legal it must be safe. Dr. Pankaj Parekh, director of the water quality division for the City of Los Angeles, has faced such criticism. The water in some city reservoirs has contained contaminants that become likely cancer-causing compounds when exposed to sunlight. To stop the carcinogens from forming, the city covered the surface of reservoirs, including one in the upscale neighborhood of Silver Lake, with a blanket of black plastic balls that blocked the sun. Then complaints started from owners of expensive houses around the reservoir. "They supposedly discovered these chemicals, and then they ruined the reservoir by putting black pimples all over it," said Laurie Pepper, whose home overlooks the manmade lake. If the water is so dangerous, why can't they tell us what laws it's violated? Dr. Parekh has struggled to make his case. "People don't understand that just because water is technically legal, it can still present health risks," he said. And so we encounter opposition that can become very personal. Some federal regulators have tried to help officials like Dr. Parekh by pushing to tighten drinking water standards for chemicals like industrial solvents, as well as a rocket fuel additive that has polluted drinking water sources in Southern California and elsewhere. But those efforts have often been blocked by industry lobbying. Drinking water that does not meet a federal health guideline will not necessarily make someone ill. Many contaminants are hazardous only if consumed for years. And some researchers argue that even toxic chemicals, when consumed at extremely low doses over long periods, pose few risks. Others argue that the cost of removing minute concentrations of chemicals from drinking water does not equal the benefits. Moreover, many of the thousands of chemicals that have not been analyzed may be harmless. And researchers caution that such science is complicated, often based on extrapolations from animal studies, and sometimes hard to apply nationwide, particularly given that more than 57,400 water systems in this country each deliver, essentially, a different glass of water every day. Government scientists now generally agree, however, that many chemicals commonly found in drinking water pose serious risks at low concentrations. And independent studies in such journals as Reviews of Environmental Contamination and Toxicology; Environmental Health Perspectives; American Journal of Public Health; and Archives of Environmental and Occupational Health, as well as reports published by the National Academy of Sciences, suggest that millions of Americans become sick each year from drinking contaminated water, with maladies from upset stomachs to cancer and birth defects. Griffin Palmer contributed reporting.