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Arsenic in well water: the best way to test, and treatment options
Arsenic is natural, invisible and common in some regions' wells. This guide covers how to test for it, how to read the number, and what state agencies say about treatment, with a source for every claim.
Why test for arsenic
- You can't tell by looking. EGLE says arsenic can't be seen or tasted in water, and a laboratory analysis designed to detect it is the only way to know the level.1
- It's common in some places. A USGS model estimates that about 2.1 million people using domestic wells in the lower 48 states (95% range about 1.5–2.9 million, 2010 population) have well water with predicted arsenic above 10 µg/L. That's our sum of the USGS county estimates.2 At the state level:
- New Hampshire estimates 25–30% of private wells have 5 ppb or more.3
- Maine's tracking program found 10% of tested wells over 10 ppb.4
- Minnesota says about 10% of private wells are over 10 µg/L.5
- In North Carolina's Union and Stanly counties, about 20% of sampled wells exceeded 10 µg/L.6
- It matters over time. Minnesota's health department says low levels over a long time are linked to diabetes and to cancers of the bladder, lungs, liver and other organs.5
The best way to test for arsenic
- Use a certified or accredited lab that's certified for arsenic. EGLE suggests calling its Drinking Water Laboratory or any commercial lab certified for arsenic, and says your local health department can provide a list.1 Minnesota points to its Environmental Laboratory Accreditation Program.5 Maine accredits labs test by test, so confirm with the lab that arsenic is covered.7
- Test at least once, then follow your state's schedule. Minnesota recommends every well be tested for arsenic at least once.5 New Hampshire, Maine and Michigan recommend arsenic testing every 3–5 years.8910 New Jersey suggests yearly arsenic testing if a past result was above 2.5 µg/L.11
- Retest a brand-new well. Minnesota says results taken when a well is built may not reflect long-term arsenic levels, and suggests retesting six months or more after drilling, especially if the result was between 5 and 20 µg/L.5
- Confirm a high result. Minnesota's advice for results above 10 µg/L applies once repeat sampling confirms them.5
- If you have treatment, test the treated water too. NHDES says to test treated water after installing a system to make sure it's working, and every 3–5 years after that.8
Reading the number
Labs report arsenic in different units. 0.010 mg/L = 10 µg/L = 10 ppb.1
| Level | What it is |
|---|---|
| 0 | EPA's health goal (MCLG) for arsenic.1 |
| 5 µg/L | New Jersey's and New Hampshire's standards for public water systems (stricter than federal). NH's took effect July 1, 2021.3 |
| 10 µg/L | EPA's enforceable standard (MCL) for public water systems.12 EGLE and Minnesota use it as the level for private-well action.15 |
| Above 100 µg/L | Maine CDC asks well owners to call before choosing treatment.13 |
Private wells aren't required to meet these standards. EGLE recommends not using well water for drinking or cooking if arsenic is above 10 µg/L.1 Minnesota recommends an alternate drinking water source or treatment that reduces arsenic once repeat sampling confirms a result above 10 µg/L.5 Minnesota also notes that drinking water below the EPA standard over many years can still increase cancer risk.5
Treatment options that agencies describe
EGLE lists these ways to reduce arsenic exposure:1
- Connect to public water, if it's available.
- Replace or modify the well to draw from a lower-arsenic aquifer. Talk to your health department first.
- Use bottled water for drinking and cooking.
- Treat the water. EGLE calls point-of-use reverse osmosis or arsenic adsorption media cartridge filters "the most effective and practical treatment method for residential use." Whole-house (point-of-entry) treatment is also an option.
Two more details from EGLE:1
- For whole-house treatment, arsenic adsorption media is generally used with low-iron water, and oxidation/filtration (greensand iron removal) with high-iron water.
- Water softeners and activated carbon filters don't reduce arsenic effectively.
Maine CDC's treatment guide lists adsorptive media, reverse osmosis and anion exchange as options for arsenic.13
Before you buy anything, EGLE recommends a unit certified by NSF for arsenic reduction, installed to its specifications, and researching its effectiveness and maintenance.1 Maine CDC suggests getting several quotes and asking about maintenance and warranty.13 Minnesota warns about water treatment scams.14
Where to get tested and treatment options
Related guides
- How to read your well water test results
- Best way to test well water
- Uranium and radon in well water
- How often to test a private well
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Michigan EGLE, "Arsenic in well water." https://www.michigan.gov/egle/about/organization/drinking-water-and-environmental-health/water-well-construction/guidance-materials/arsenic-in-well-water ↩↩↩↩↩↩↩↩↩
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Ayotte, J.D., Medalie, L., and Qi, S.L., 2017, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter based on probability estimates for the conterminous U.S., U.S. Geological Survey data release (sum of county estimates). https://doi.org/10.5066/F7CN724V ↩
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NHDES, "More Protective Arsenic Standard Will Reduce Risk for Many" (March 8, 2021). https://www.des.nh.gov/news-and-media/blog/more-protective-arsenic-standard-will-reduce-risk-many ↩↩
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U.S. CDC, "About Maine Tracking Program." https://www.cdc.gov/environmental-health-tracking/php/our-work/about-maine-tracking-program.html ↩
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Minnesota Department of Health, "Arsenic in Drinking Water." https://www.health.state.mn.us/communities/environment/water/contaminants/arsenic.html ↩↩↩↩↩↩↩↩↩
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Sanders, A.P., and others, 2012, "Arsenic in North Carolina: public health implications," Environment International (Table 1). https://pmc.ncbi.nlm.nih.gov/articles/PMC3539775/ ↩
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Maine CDC, "Maine In-State Commercial Drinking Water Labs" (PDF). https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/CommercialListMaineLabs.pdf ↩
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NHDES, "Water Testing Guidance for Private Well Users" (April 2026). https://www.des.nh.gov/sites/g/files/ehbemt341/files/documents/labs-private-wells.pdf ↩↩
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Maine CDC, "Private Well Water." https://www.maine.gov/dhhs/mecdc/healthy-living/health-and-safety/drinking-water-safety/private-well-water ↩
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Livingston County, MI, Environmental Health, "Water Quality Testing for Wells" (MDHHS schedule). https://milivcounty.gov/environmental-health/wells/water-quality/ ↩
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NJDEP, "Private Wells: Arsenic." https://dep.nj.gov/privatewells/arsenic/ ↩
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U.S. EPA, "National Primary Drinking Water Regulations." https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations ↩
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Maine CDC, "Quick Guide to Well Water Treatment" (PDF). https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/Well-water-treatment8.27.2026.pdf ↩↩↩
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Minnesota Department of Health, "Home Water Treatment Facts." https://www.health.state.mn.us/communities/environment/water/factsheet/hometreatment.html ↩