Safe drinking water is something we Americans tend to take for granted, until a crisis like the lead contamination in Flint, Michigan, makes us wonder what chemicals could be lurking in our own taps. “Flint was a wake-up call for Americans, but it’s not the only place in the United States with tap water problems,” says Erik Olson, director of NRDC’s Health program. “Thousands of other cities and small towns across the country are serving water with lead or other contamination problems to millions of people.” The NRDC Health team has fought to protect drinking water—both locally and nationally—for decades. In fact, Lynn Thorp, national campaigns director for the nonprofit organization Clean Water Action, says NRDC has been the group’s most valued partner in efforts to enforce the federal Safe Drinking Water Act. “Together we’ve been a watchdog for the public at every stage of implementation and for all the many parts of the law,” she says. While there have been victories over the years, you should still remain vigilant about the contaminants that might be in your pipes, faucets, or local water supply. Here’s what you should know and how you can stay safe. It’s not just about lead All public water suppliers in the United States are required to uphold certain levels of water quality. As long as these requirements are met, Olson says, most Americans can drink their local tap water without worry. Still, violations remain widespread, and some water systems have contaminants that aren’t regulated by the U.S. Environmental Protection Agency. According to a new NRDC report, nearly 77 million Americans got drinking water from systems that violated federal protections in 2015, and more than a third of this number relied on systems that did not comply with standards put in place to protect health. Millions of other Americans’ water suppliers failed to test water safety properly or didn’t report test results to health authorities or customers—potentially sweeping many more health risks under the rug. Turning on the Tap in America LEARN MORE These numbers likely understate the extent of the problem, given underreporting and the fact that many contaminants aren’t even monitored or regulated. For instance, common contaminants such as perchlorate and PFOA/PFOS (chemical cousins of Teflon) occur in millions of Americans’ tap water, but because they aren’t regulated by the EPA, they don’t show up in these already staggering figures. Sensitive groups, like pregnant women and children, are at higher risk for health complications, especially from the following contaminants: Lead: Likely the most famous bad guy, this heavy metal can leach from lead pipes and plumbing fixtures, especially when the water flowing through them is corrosive. It can cause neurological and behavioral problems in children and adverse health effects in adults. “It’s a more common problem in cities with older water systems,” NRDC Health team scientist Kristi Pullen Fedinick says, “but what a lot of people don’t realize is that even relatively new brass fixtures and faucets can still contain significant amounts of lead. Just because your home is less than 20 years old doesn’t necessarily mean you’re lead-free.” Atrazine: This endocrine-disrupting chemical is one of the most commonly detected pesticides in U.S. waters. NRDC studies have found its contamination is most common in drinking water across the Midwest and the southern United States. The EPA currently monitors a sample of community water systems to determine if atrazine concentrations pose a risk to public health, but NRDC has called on the government to phase out the use of this chemical entirely. Pathogens: Bacteria, viruses, and parasites that cause illness can find their way into water supplies that are inadequately treated to kill germs. Fortunately, these pathogens are much better controlled today than they once were. After a 1993 waterborne-disease outbreak in Milwaukee sickened more than 400,000 people, Olson says, “NRDC really led the charge in changing the EPA’s rules and safeguards.” But clearly much more remains to be done. Chlorine treatment by-products: Chemicals used in drinking water’s disinfection process, such as trihalomethanes and haloacetic acids, may cause cancer and reproductive problems if present in high quantities. Arsenic: The EPA estimated in 2000 that nearly 36 million Americans drank water containing arsenic at or above 3 parts per billion—the level NRDC had urged be established as a drinking water standard. “The EPA had delayed and delayed updating the arsenic standard that was originally issued in the 1960s, but we finally got them to relent and update the arsenic number based on modern science in the early 2000s,” Olson says. Since then, arsenic levels across the country have declined as a result, he adds, but the contaminant is still worth looking out for. Nitrates: Though nitrates occur naturally in plants and soil at low concentrations, they have become a widespread contaminant due in part to their use as fertilizer. Runoff from factory farms flows into surface and groundwater and ends up in our drinking water. The EPA set a limit of 10 parts per million for nitrates, which can be harmful to pregnant women and infants. In rare cases, exposed infants can develop blue baby syndrome, a potentially fatal illness that prevents the blood from carrying oxygen. Radioactive contaminants: Most radioactive elements found in drinking water occur naturally, but radioactive material from the production of nuclear weapons, energy, and medicines can also get into drinking supplies through leaks or improper waste storage. Exposure can cause cancer or kidney failure. Vinyl chloride: Used to make PVC plastic products, such as some pipes, this cancer-causing contaminant can leach from older PVC piping and has been found in the drinking water of a small number of communities across the country. Perchlorate: This widespread toxic chemical, used in rocket fuel, explosives, and road flares, can interfere with thyroid hormone production. Perchlorate has been detected in the water in at least 26 states, yet there is no federal standard for its presence in drinking water. In 2011, after more than a decade of pressure from environmental and health groups led by NRDC, the EPA announced that it would set such a standard—but it still hasn’t even proposed a rule for the contaminant. After NRDC filed