EWG's Tap Water Database




Arsenic is a naturally occurring mineral that causes bladder, lung and skin cancer, as well as harm to the skin and lungs. Arsenic is found in drinking water in at least 48 states, and can also contaminate food, particularly rice and rice-based products.

In 2001, the EPA set a legal limit for arsenic in drinking water of 10 parts per billion, or ppb. But the EPA’s analysis showed that this limit was not low enough to protect public health, potentially causing up to 600 cancer cases in 1 million people who drink arsenic- contaminated water for a lifetime. A more recent EPA analysis, from a 2010 draft report, suggests that arsenic is much more toxic than previously estimated.

EWG supports California’s public health goal of a maximum of 0.004 ppb, or 4 parts per trillion, of arsenic in drinking water, corresponding to a one-in-a-million cancer risk. EWG urges the federal government to lower its limit and help water utilities invest in treatment methods to reduce exposure.

Click here to see the nationwide testing results for arsenic.

How does arsenic get into drinking water?

The EWG Tap Water Database shows that in 2015, over more than 70 million Americans received water with arsenic exceeding the California public health goal. These estimates don’t include people who get their drinking water from private wells that might have unsafe levels of arsenic.

Arsenic in drinking water comes from natural, industrial and agricultural sources. It leaches from rocks into groundwater that might be used for drinking or irrigation. Arsenic levels in water tend to be highest in the Western states, though arsenic also causes water quality problems in parts of the Midwest and Northeast.

Mining waste, metal production, coal power plants and burning of other fossil fuels are additional sources of arsenic pollution. Arsenic contaminates soil and water in orchards and farm fields where it was previously used as a pesticide. Arsenic was intentionally added to poultry feed until the Food and Drug Administration banned this practice in 2013. Arsenic was also formerly used as a lumber preservative, which has contaminated soil in many residential areas and playgrounds.

How can I be exposed to arsenic?

Both food and water are major sources of arsenic for Americans. Arsenic can be found in fruits and vegetables and in rice-based foods. Rice plants naturally accumulate arsenic from water and soil, and are the dominant source of arsenic in the American diet. Certain seaweeds have high arsenic levels, and seafood has an arsenic-based sugar that is believed to be less toxic than the so-called inorganic forms of arsenic that contaminate water sources.

Arsenic concentrations in U.S. drinking water are highly variable. A 2014 study by Margaret Kurzius-Spencer of the University of Arizona found that when drinking water levels of arsenic are above 10 ppb, water is the dominant source of exposure; when levels in water are below 10 ppb, food is the main source of arsenic.

Because arsenic is in tobacco smoke, smokers have higher exposures and a greater risk of arsenic-related disease. People with jobs in mining or metal smelting, semiconductor production, or working with arsenic-treated wood are at higher risk of exposure.

Why is arsenic harmful to health?

Both the EPA and the World Health Organization have determined that arsenic is a “known human carcinogen” based on indisputable evidence that arsenic exposures increase the risk of bladder, lung and skin cancers. Other evidence suggests it can cause liver, kidney and prostate cancers. Arsenic can also cause skin lesions, harm to the kidneys and other internal organs, and cardiovascular disease. Some studies have found lung cancer risks associated with drinking water exposures. The lung cancer risks are especially high for smokers who also have arsenic in their drinking water.

The need for a more health protective arsenic standard was shown by studies from the National Cancer Institute and academic researchers. A study led by Dalsu Baris, formerly of the National Cancer Institute, found that people drinking water from private wells in the Northeast had elevated risks of bladder cancer even when the estimated arsenic levels were below the legal limit.

Animal and human studies suggest that the cancer-causing effects of arsenic are particularly severe when exposures take place during pregnancy and early childhood. A 2013 study by Marisa Naujokas, of the MDB consulting firm in North Carolina, found that prenatal exposure can not only increase cancer risk, but impair intelligence, cause behavioral problems and harm the developing immune system.

How much is arsenic harmful to health?

The EPA sets a legal limit of 10 ppb for arsenic in drinking water. But that concentration still puts many Americans at risk – as many as 600 cancer cases for every million people who have arsenic in their water. In 2010 the EPA’s Integrated Risk Information System program reassessed the potency of arsenic and determined it was 17 times more toxic than previously estimated. However, due to political pressure, the EPA has not finalized this draft assessment.

EWG agrees with the California Office of Environmental Health Hazard Assessment determination that arsenic concentrations in water would ideally be below 0.004 ppb to reduce lifetime cancer risk to one in a million. Limiting arsenic in drinking water is prudent given that people are also exposed through their diets, including through otherwise healthy foods.

What should be done to reduce public exposure to arsenic?

The EPA must lower the legal limit for arsenic in drinking water, work with water utilities to filter out arsenic, and help inform people drinking well water of when they might be at risk.

Public health agencies must also work to reduce arsenic in food and educate the public about the risks from otherwise healthy foods. The FDA has set a guideline for arsenic in fruit juice and proposed a limit for arsenic in rice cereal for infants, but neither will have a meaningful effect on levels in these foods, let alone the overall food supply.

What can I do to reduce my own exposure?

You can find out if arsenic contamination is a problem in your drinking water by checking EWG’s Tap Water Database or contacting your water company. If you drink well water, you can find out if arsenic is a problem in your region by contacting your local health department. Simple carbon water filters will not remove arsenic. Consult EWG’s water filter guide to find an option that works for arsenic, such as reverse osmosis or carbon block technologies.

You can also reduce your arsenic exposure by limiting consumption of certain foods. EWG’s Food Scores database explains more about the issue of arsenic contamination in rice-based foods. Arsenic accumulates at relatively high levels in rice, so do your best to avoid rice-based processed foods like crackers, cereals, pastas, and foods sweetened with rice syrup. Do not feed infants and children rice-based cereals or use rice milk as a substitute for milk. Whole grain rice is a dietary staple for millions of Americans, so it isn’t easy for many families to reduce their consumption.


D. Baris et al., Elevated Bladder Cancer in Northern New England: The Role of Drinking Water and Arsenic. Journal of the National Cancer Institute, 2016, 108(9). pii: djw099.

EPA, Drinking Water Arsenic Rule History. Available at

EPA, Office of Research and Development, Assessment Development Plan for the Integrated Risk Information System (IRIS) Toxicological Review of Inorganic Arsenic. 2015. Available at

EPA, Inorganic Arsenic Meetings and Webinars. 2017. Available at

FDA, Arsenic-Based Animal Drugs and Poultry. Available at

M. Kurzius-Spencer et al., Contribution of Diet to Aggregate Arsenic Exposures –An Analysis Across Populations. Journal of Exposure Science and Environmental Epidemiology, 2014, 24:156-162.

M.F. Naujokas et al., The Broad Scope of Health Effects from Chronic Arsenic Exposure: Update on a Worldwide Public Health Problem. Environmental Health Perspectives, 2013, 121(3):295-302. Available at

World Health Organization, International Agency for Research on Cancer, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100C. Arsenic, Metals, Fibres, and Dusts. 2012. Available at