Contaminants in Water
Environmental Health Division
Arsenic in Drinking Water
Arsenic occurs naturally in rocks and soil across Minnesota. Small amounts can dissolve into groundwater that may be used for drinking water. Drinking water with arsenic in it can increase your risk of cancer and other serious health effects. It is important to know how much arsenic is in your drinking water and how you can reduce your exposure.
This information is also available as a PDF document: Arsenic in Drinking Water (PDF)
Drinking water with low levels of arsenic over a long time is associated with diabetes and increased risk of cancers of the bladder, lungs, liver, and other organs. Coming in contact with arsenic can also contribute to cardiovascular and respiratory disease, reduced intelligence in children, and skin problems, such as lesions, discoloration, and the development of corns.
Health impacts of arsenic may not occur right away and can develop after many years, especially if you are in contact with arsenic at a low level over a long time.
The Environmental Protection Agency (EPA) federal drinking water standard for arsenic in drinking water is 10 micrograms per liter (µg/L).* However, drinking water with arsenic at levels lower than the EPA standard over many years can still increase your risk of cancer. As a result, EPA sets health risk goals. The EPA has set a goal of 0 µg/L for arsenic in drinking water. These goals do not consider the cost of water treatment to reach that level of arsenic in drinking water.
*One microgram per liter (µg/L) is the same as 1 part per billion (ppb).
If you have a private well
The Minnesota Department of Health (MDH) recommends that every well be tested for arsenic at least once. When a new well is drilled, the well contractor will test for arsenic and share the results with you and MDH. Test results taken when a new well is constructed may not accurately measure long-term arsenic concentrations. You may want to re-test your well for arsenic six months or more after the well is drilled, especially if the test results were between 5 and 20 µg/L. Owners of existing wells are responsible for testing their own drinking water for arsenic. You can find certified laboratories that test for arsenic through the Environmental Laboratory Accreditation Program. You can also contact your county to see if they have any programs to make testing your water easier.
If tests do not find arsenic in your well water, further testing is not necessary. If tests detect arsenic at levels above 10 µg/L, and repeat sampling confirms the results, MDH recommends that you use an alternate source of drinking water or install a treatment system that reduces arsenic. For more information on home water treatment, visit Home Water Treatment. Let your medical provider know if you have been drinking water with levels of arsenic above 10 µg/L.
Contact MDH (651-201-4700 or firstname.lastname@example.org) with questions.
If you are on a public water system
The EPA has a federal drinking water standard of 10 µg/L for public water systems serving places where people live, work, go to school, and receive childcare. These systems take action to reduce arsenic if levels exceed the standard.
You can find the level of arsenic in a community water system (serving where you live) by reading their water quality report (also known as a Consumer Confidence Report [CCR]). You can call your public water system to get a paper copy of your CCR or you can find it online at Find Your Local CCR.
If you want to take additional steps to reduce your exposure to arsenic in drinking water, you can use a home water treatment system. For more information on home water treatment, visit Home Water Treatment Units: Point-of-Use Devices.
Non-community systems serving schools, offices, factories, and childcare facilities test for arsenic; you can contact your non-community system to find the level of arsenic detected in the system. Non-community systems serving restaurants, resorts, and campgrounds are not required to test for arsenic.
Reducing Other Contact with Arsenic
You may come into contact with arsenic in ways other than drinking water. Reduce your contact with arsenic by following the tips below:
- Do not burn wood that is or may be treated with arsenic. Throw away arsenic-treated wood in the trash with other solid waste. If you don’t know if wood has been treated with arsenic, don’t burn it.
- Know the ingredients of all medications or health remedies you use, especially “folk” remedies.
- Seal decks or other wood structures treated with arsenic every six months to two years.
- Make sure children wash their hands after playing on play structures or decks that have arsenic-treated wood.
- Wash and peel vegetables grown in soil, especially in urban gardens.
- Eat less rice, cereal grains, or other foods that contain arsenic.
- Check old pesticides and soil supplements to see if they contain arsenic. If you are not sure, don’t use them.
Arsenic occurs naturally in soil and rock. Arsenic from soil and rock can dissolve into groundwater and enter drinking water wells. For most people, food and water are the biggest sources of exposure to arsenic.
There are two forms of arsenic:
- Inorganic arsenic is formed when arsenic combines with metals and elements other than carbon. Inorganic arsenic is the type found in contaminated drinking water, and is the most harmful type of arsenic. This type of arsenic is also found in rice, cereal grains and other foods.
- Organic arsenic is formed when arsenic combines with carbon. It is the most common type of arsenic found in food. It is common in fish and shellfish, and is less harmful to health than inorganic arsenic.
Some arsenic in the environment comes from human activity. Arsenic was an ingredient in some pesticides and was used as a wood preservative for wood foundations, decks, and children’s outdoor play structures.
Arsenic can be found in groundwater throughout Minnesota but is more likely in some areas than others. Approximately 10 percent of private drinking water wells in Minnesota have arsenic levels higher than 10 µg/L. Some wells have levels as high as 350 µg/L, however most results are below 50 µg/L. Arsenic levels can vary between wells, even within a small area.
You can see a map of arsenic levels in private wells on the MN Public Health Data Access Portal.
Few public water systems have detected arsenic levels above the EPA standard. If a system detects arsenic levels above the standard, MDH works with the system to reduce the level.
MDH regulates public water systems by:
- Approving public water systems’ treatment plans
- Enforcing the Safe Drinking Water Act
- Testing public water supplies
MDH regulates private and public wells through:
- Establishing and enforcing Laws and Rules for proper Construction of Wells and Borings and Sealing of Wells and Borings
- Providing guidance for private well owners on Water Quality/Well Testing/Well Disinfection
MDH is also using Clean Water Funds to conduct a Private Well Protection Arsenic Study to better understand how water sampling methods and timing impact arsenic test results.