When water flows out of the faucet and into a glass, it usually appears clean and healthy. A report released Wednesday, though, found hundreds of harmful contaminants across the American water supply that can cause cancer, developmental issues in children, problems in pregnancy and other serious health conditions.

"There are chemicals that have been linked to cancer, for example, that are found above health-based limits, or health guidelines, in the water of more than 250 million Americans," said Nneka Leiba, director of Healthy Living Science at the Environmental Working Group, or EWG, an independent nonprofit organization that released a detailed account of the contaminants. Other substances found in the water of millions of Americans can profoundly impact our health. Lead has been linked to behavior problems in kids, polyfluorinated chemicals are tied to altered thyroid function, and nitrosamines can damage DNA. (For more national stories, subscribe to the Across America Patch and receive daily newsletters and breaking news alerts.)

EWG, in conjunction with outside scientists, assessed health-based guidelines for hundreds of chemicals found in our water and compared them to the legal limits. The law often permits utilities to allow these dangerous chemicals to pollute our waters. "Legal is not safe," said Leiba. "In many cases, it's far from safe."

In the case of trihalomethanes, the carcinogen in the water of more than 250 million Americans, the legal limit is 100 times higher than safety guidelines. Some contaminants in our nation's water supply violate both legal and health guidelines. In May, Fairchild Air Force Base in Washington state discovered extremely high levels of the substances PFOA and PFOS, artificial chemicals linked to multiple forms of cancer, in local drinking water wells. Airway Heights, a nearby city where around 6,000 people people live, tested its water and found high levels of contamination as well. Locals were forced to start boiling their water on their own and using free bottled water provided by the base.

While this contamination event was particularly severe, water across the country carries serious risks. "There are more than 250 contaminants across our nation's drinking water," Nneka Leiba, director of Healthy Living Science at EWG, told Patch. "About 160 of those are unregulated. And that's a big concern, because if a chemical is unregulated, that means it can be present in our water at any level — and be legal." Most of the water in the United States comes from local utilities that measure contaminants in their water supply, but this data can be difficult to obtain. (More below)

Contaminants in your water: EWG has released a public database cataloguing contaminants in water systems in every state in the country — the first comprehensive database of its kind that took two years to build. First select the state where you live, and you'll see state-level data. For more local information, enter your zip code. After you enter your zip code, you'll be directed to a page showing the water utilities in your county. Select your town to see which contaminants put your families at risk.

No single group has collected all this information for all 50 states in an easily searchable database — until now. And it's incredibly easy to use it to see what contaminants are coming through your faucet. Drinking water. Photo credit: Pixabay The Risks

While we know our water supply is full of harmful chemicals, scientists struggle to quantify the wide-scale effects of the hundreds of contaminants people are drinking across the country. Leiba said that cancer rates have gone up in recent years, as the World Health Organization confirms, even as the death rate from cancer have declined overall. It's impossible to know for sure how large a part water contaminants play in the increased prevalence of the disease. But this uncertainty, Leiba said, is "another reason why precaution is so necessary." Becoming aware of the dangers is an important step. Here's a short list of just some of the chemicals that endanger the health of children, pregnant women and the population at large: Trihalomethanes and other disinfection byproducts — These substances are created when disinfection chemicals, like chlorine, bind with organic matter in water. While it's a good thing that water is disinfected, the byproducts of this reaction have been linked to liver cancer, kidney cancer, intestinal tumors, miscarriage and other difficulties in pregnancy. EWG found the chemical in the water of more than 280 million Americans.

and other disinfection byproducts — These substances are created when disinfection chemicals, like chlorine, bind with organic matter in water. While it's a good thing that water is disinfected, the byproducts of this reaction have been linked to liver cancer, kidney cancer, intestinal tumors, miscarriage and other difficulties in pregnancy. EWG found the chemical in the water of more than 280 million Americans. Nitrates — A byproduct of animal waste and agricultural fertilizers, nitrates have the potential to increase the rate of cancer, according to the National Cancer Institute. EWG say nitrates are found in water serving almost 218 million Americans.

— A byproduct of animal waste and agricultural fertilizers, nitrates have the potential to increase the rate of cancer, according to the National Cancer Institute. EWG say nitrates are found in water serving almost 218 million Americans. Perfluorooctanoic acid (PFOA) — PFOA is a man-made chemical that is found in low levels in most everyone's blood, according to the American Cancer Society. It is typically found in low levels in drinking water, but it can spike in certain areas. Some studies have linked it to cancers of the kidney, thyroid, prostate, bladder and ovaries. EWG found that around 7.5 million people are served by water systems with elevated levels of PFOA.

(PFOA) — PFOA is a man-made chemical that is found in low levels in most everyone's blood, according to the American Cancer Society. It is typically found in low levels in drinking water, but it can spike in certain areas. Some studies have linked it to cancers of the kidney, thyroid, prostate, bladder and ovaries. EWG found that around 7.5 million people are served by water systems with elevated levels of PFOA. Lead — Lead was the chemical culprit in the water crisis that devastated Flint, Michigan, and continues to haunt the city to this day. The law requires utilities to act when lead levels reach 15 parts per billion in the water supply, even though the government says that there's no level of lead that is safe. It can cause learning and behavioral disabilities, short height, hearing impairments and other difficulties, especially in children. While utilities track levels of lead in their water, it may also be present in your home or neighborhood's pipes, which is more difficult to monitor. About half a million children are believed to have blood lead levels that the Centers for Disease Control and Prevention considers "elevated."

— Lead was the chemical culprit in the water crisis that devastated Flint, Michigan, and continues to haunt the city to this day. The law requires utilities to act when lead levels reach 15 parts per billion in the water supply, even though the government says that there's no level of lead that is safe. It can cause learning and behavioral disabilities, short height, hearing impairments and other difficulties, especially in children. While utilities track levels of lead in their water, it may also be present in your home or neighborhood's pipes, which is more difficult to monitor. About half a million children are believed to have blood lead levels that the Centers for Disease Control and Prevention considers "elevated." Arsenic — Arsenic is a naturally occurring chemical that is highly carcinogenic. It is very common in our water systems, and it sometimes goes overlooked in private wells. Since there is no safe level of arsenic in drinking water, even a small amount poses serious risks of cancer and other illnesses. EWG found arsenic is present in the water supply of 70 million Americans. Free bottled water offered to residents of Flint, Michigan, in response to the contaminated water crisis. Photo by Bill Pugliano/Getty Images In any individual case, it may be difficult to link a specific contaminant to the development of cancer or other adverse conditions. However, we can be confident that as long as substantial levels of harmful chemicals are in our environment and drinking water, the country as a whole will be sicker and worse off. What You Can Do Once people know about the high levels of dangerous contaminants lurking in their water, the question becomes what they can do to protect their health. "There's a way to reduce those levels simply by buying a water filter," said Leiba. "We don't want to scare the population by saying there are 250 chemicals and just leaving it there," she continued. "As a consumer you may look at it and get a little overwhelmed." For this reason, EWG provides a guide to finding water filters. Its website allows you to search for filters that block particular chemicals and pollutants. If you find that your local water supply has a particularly high level of a dangerous chemical, you can search for a filter that blocks that substance. There are many types of filters, including carbon filters, deionization filters and distillation filters. Each type has its own strengths and weakness, so sometimes a filter will include multiple filtration methods to eliminate more potential threats. To find the most effective filter, look for certifications from the Water Quality Association and NSF International. Different filters remove different contaminants. It's important to remember, though, that even high-quality filters are not 100 percent effective. "Filters don't remove everything," Scott Meschke, professor of environmental and occupational health sciences at the University of Washington, told Patch. He emphasized that it's important to make sure you're using a filter that is designed to fit your local needs.