Arsenic in Well Water - EH: Minnesota Department of Health

Arsenic in Well Water
Well Management Program

Arsenic occurs naturally in rocks and soil across Minnesota and can dissolve into groundwater. Drinking water that contains arsenic can increase your risk of cancer and other serious health effects. Unfortunately, there is no way to know the arsenic level in water before a well is drilled. Arsenic levels can vary between wells, even within a small area. You cannot taste, see, or smell arsenic in your water.

Test your well for arsenic at least once so you know how much arsenic is in your drinking water and you can make an informed decision about whether to take further action.

Drinking Water Standard

The maximum level of arsenic the U.S. Environmental Protection Agency (EPA) allows in community water systems is 10 micrograms per liter (µg/L*). However, consuming water with arsenic at levels lower than the EPA standard over many years can still increase your risk of cancer. As a result, the EPA has set a goal of 0 µg/L of arsenic in drinking water.

*1 µg/L is the same as 1 part per billion (ppb).

Health Risks

Consuming water with even 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. Ingesting 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 take many years to develop.

Test Your Well Water

Test for arsenic at least once.

Minnesota Department of Health (MDH) recommends you use an accredited laboratory to test your water. Contact an accredited laboratory to get sample containers and instructions, or ask your county environmental or public health services if they provide well testing services.

Accredited Labs in Minnesota Accepting Samples from Private Well Owners [PDF].

New wells are tested for arsenic.

As of August 2008, well contractors test each newly drilled well for arsenic and share the results with the well owner and MDH.

Find existing test results: Use the online Minnesota Well Index or contact MDH for test results for a well constructed since 2008.

Consider confirming the arsenic level.

  • If arsenic was NOT detected in the first sample, your water is unlikely to have arsenic later.
  • If arsenic was detected in your new well, you may want to retest your well about six months after construction. MDH research found that when arsenic is detected in a new well, the level may increase or decrease in the first few months after construction. Learn more about this study at Private Well Protection Arsenic Study.

Learn more about testing well water at Well Testing, Results, and Options.

Protect your health! Test your well water for: Coliform Bacteria (every year), Nitrate (every other year), Arsenic (at least once), Lead (at least once), Manganese (before a baby drinks the water). Testing is even more important if young children drink the water.

MDH may recommend you test for additional contaminants based on where you live.

Protect Your Family

If arsenic is detected at any level, consider:

  • Installing a treatment unit or
  • Using a different drinking water source.

Drinking water with arsenic over many years increases the risk of diseases such as cancer.

MDH highly recommends you take action if arsenic levels are above 10 µg/L.

Water Treatment Units that Reduce Arsenic:

  • Reverse osmosis uses energy to push water through a membrane with tiny pores. The membrane stops many contaminants while allowing water to pass through.
  • Distillation uses distillers to boil water, which makes steam. The steam rises and leaves contaminants behind. The steam hits a cooling section, where it condenses back to liquid water.
  • Adsorptive media is a charged media bed that causes ions of the opposite charge (contaminants) to be pulled out of the water and attach to the media.  
  • Anion exchange removes dissolved minerals in the water. The owner adds sodium chloride or potassium chloride (salt), which replaces negatively charged minerals in the water.
  • Ozonation and filtration is a system in which ozone (a disinfectant that kills bacteria and viruses) is generated using electricity and then injected into the water. The ozone changes dissolved contaminants into solid particles. The solid particles are large enough to be filtered out of the water.
  • Oxidation filtration has a media bed that changes dissolved contaminants into solid particles. The solid particles are large enough to be filtered out of the water.
  • Chlorination and filtration requires that the owner add chlorine bleach to a holding tank. A pump feeds chlorine into the water, which helps change dissolved contaminants into solid particles. The solid particles are large enough to be filtered out of the water.

Learn more about these treatment options, pros and cons, and general costs at the Home Water Treatment webpage. A water treatment specialist can help you select the best option for your household.

MDH recommends that you choose a treatment system that is certified by an independent certifying organization, such as NSF International, Underwriter’s Laboratory (UL), or the Water Quality Association, that tests water treatment systems to assure their effectiveness in living up to the manufacturer’s claims. In Minnesota, water treatment systems must be installed by a licensed and bonded plumbing or water conditioning contractor, although homeowners may install equipment in homes they own and occupy. After the treatment system is installed, it is important to follow the manufacturer’s recommendations for maintaining the system. Also, have the treated water tested periodically to make sure that the treatment system is working properly.

Remember that while some treatment systems can be useful for other purposes, systems such as conventional water softeners and activated carbon filters will not alone remove arsenic. Also, boiling the water will only concentrate the arsenic, due to evaporation of some of the water.

Using a Different Drinking Water Source

There are a few options for using a different drinking water source to reduce your exposure to arsenic in your drinking water.

Construct a New Well

In some areas, a new well constructed into a different water-bearing formation may produce water with less natural arsenic. Drilling a new well may be a good option if you already want to replace your existing well for other reasons. It can be less expensive in the long run than maintaining a treatment system. However, a new well may still contain natural arsenic even if the well is properly constructed and in an appropriate location.

As our information about the occurrence of arsenic grows, we will learn more about which water-bearing formations in an area have higher or lower levels of arsenic. While there will still be no guarantees, the chances of constructing new wells with lower arsenic levels should improve in some areas. For more information about new well construction, contact a licensed well and boring contractor (Licensed Well and Boring Contractor Directory) or a well specialist at your nearest MDH district office (Contacting the Well Management Section).

Connect to a Community Public Water System

In some cases, connection to a community public water supply system may be possible. All community public water systems are regularly tested for arsenic and other contaminants and must comply with all EPA standards.

Buy Bottled Water

If the level of arsenic in your well water is above 10 µg/L, you could reduce arsenic levels in your drinking water by using bottled water. It is important to note that while all public drinking water systems must meet EPA standards, no single set of standards applies to all bottled water. Instead, bottled water is subject to a variety of standards, depending on the type of bottled water and where it is bottled. These standards may be more or less stringent than those for public water systems. If you are considering switching to bottled water, be sure that levels of arsenic and other contaminants in the bottled water you choose are lower than levels in water from your current water supply. The bottling company should be able to provide testing results for their water. Learn more about bottled water at Bottled Water: Questions and Answers.

Water with Arsenic is Safe to use for Other Things (Unless the Level is Above 500 µg/L.)

Since your skin does not easily absorb arsenic, your water is safe for washing dishes and clothes, brushing teeth, showering, bathing, and watering plants (including vegetables).

Tips for Reducing Other Contact With Arsenic

  • Do not burn wood treated with arsenic.
  • Be aware of ingredients in medications and folk remedies.
  • Seal arsenic-treated wood structures.
  • Make sure children wash their hands.
  • Wash and peel vegetables grown underground (e.g., potatoes, carrots).
  • Eat less rice, cereal grains, or other foods that contain arsenic.
  • Do not use old pesticides and soil supplements if they contain arsenic.

Learn more tips for reducing other contact with arsenic at Arsenic and You.

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Arsenic in Minnesota Water

Arsenic has been detected in about 40 percent of new wells drilled since 2008 in Minnesota. (The detection level for arsenic is usually 2 µg/L.) About 10 percent of Minnesota’s private wells have arsenic levels higher than 10 µg/L.

Arsenic is in groundwater throughout the state, but it is more likely in some areas. The map below shows where arsenic is found most often in Minnesota wells. (Map made with MDH data from 2008-2017.) You can learn more about arsenic levels in private wells in your county at MN Data: Private Wells-Arsenic.

Map shows the percent of new wells with arsenic detections in Minnesota. The counties with the highest percentage of new wells with arsenic detections are in central and west central Minnesota.

The way glaciers moved across Minnesota affects where arsenic is found in sediment and groundwater. Arsenic levels can vary between wells, even within a small area. Some wells have arsenic levels as high as 350 µg/L. Learn more about arsenic in private well water through the The Minnesota Arsenic Study (2000).

Background Information

For most people, food and water are the biggest sources of arsenic exposure. There are two forms of arsenic:

  • Inorganic arsenic is the type found in drinking water and is the more harmful type of arsenic. It is also found in rice, cereal grains, and other foods. It forms when arsenic combines with metals and elements other than carbon.
  • Organic arsenic 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. It is formed when arsenic combines with carbon.

While most arsenic in Minnesota’s environment occurs naturally, some comes from human activity. Arsenic was an ingredient in some pesticides and was used as a wood preservative in the past.

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Should I test my well water for anything besides arsenic?

Yes. Both natural sources and human activities can contaminate well water and cause short- or long-term health effects. Testing your well water is the only way to detect most of the common contaminants in Minnesota groundwater; you cannot taste, see, or smell most contaminants. Minnesota Department of Health recommends testing for:

  • Coliform bacteria every year and any time the water changes in taste, odor, or appearance. Coliform bacteria can indicate that disease-causing microorganisms may be in your water.
    See Bacterial Safety of Well Water.
  • Nitrate every other year. Bottle-fed infants under six months old are at the highest risk of being affected by levels of nitrate higher than 10 milligrams per liter in drinking water.
    See Nitrate in Well Water.
  • Lead at least once. The well and water system may have parts that have lead in them, and that lead can get into drinking water. Lead can damage the brain, kidneys, and nervous system. Lead can also slow development or cause learning, behavior, and hearing problems.
    See Lead in Well Water Systems.
  • Manganese before a baby drinks the water. High levels of manganese can cause problems with memory, attention, and motor skills. It can also cause learning and behavior problems in infants and children.
    See Manganese in Drinking Water.

Other contaminants sometimes occur in private water systems, but less often than the contaminants listed above. Consider testing for:

  • Volatile organic chemicals if the well is near fuel tanks or a commercial or industrial area.
  • Agricultural chemicals commonly used in the area if the well is shallow and is near cropped fields or handling areas for agricultural chemicals or is in an area of geologic sensitivity (such as fractured limestone).
  • Fluoride if children or teenagers drink the water.

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Updated Tuesday, 17-Dec-2019 15:28:00 CST