Arsenic in Well Water: Safe Levels, Testing and How to Remove It
Arsenic is one of the few well water problems you cannot see, smell or taste. A glass of water with five times the safe level looks exactly like clean water.
In this guide I explain the safe limit, how to read your lab number, and the treatments that actually work. Use the checker below to see where your result stands and what to do next.
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What to know
- The EPA limit is 10 ppb (0.010 mg/L). About 7% of sampled wells in the main US aquifers exceed it, according to the USGS.
- Arsenic comes mostly from natural rock, so a lab test is the only way to know your level.
- Do not boil water for arsenic. It does not remove it.
- Above 10 ppb, reverse osmosis at the kitchen tap is the usual fix. Arsenic III needs oxidizing first for best results.
Arsenic Result Checker
Enter the total arsenic number from your lab report. Labs use ppb, µg/L or mg/L, so pick the unit on your report.
Guidance only, based on EPA, USGS, Connecticut Department of Public Health and Penn State Extension advice. Follow your state health department for your own well.
The Safe Limit for Arsenic in Well Water
The EPA set the maximum level for arsenic in public drinking water at 10 parts per billion in 2001, down from 50. Private wells are not regulated, but state health departments use the same 10 ppb number as the point to act.
| Your result | What it means | What to do |
|---|---|---|
| Under 1 ppb | Very low or not detected | Retest after major changes to the well |
| 1 to 10 ppb | Detected, under the federal limit | Retest about every 5 years; check your state, as New Jersey uses 5 ppb |
| Over 10 ppb | Above the EPA limit | Bottled or treated water for drinking and cooking; fit treatment |
| Over 500 ppb | Very high | Call your health department before choosing treatment |
Long term exposure is linked to bladder, lung, liver and skin cancer, as well as heart and skin problems. That is why the advice is to act on the number, not on how the water tastes.
Where Arsenic in Well Water Comes From
Most arsenic in wells comes from the rock and sediment the aquifer runs through, not from pollution. The USGS found arsenic at 1 ppb or more in nearly half of sampled wells, and estimates about 2.1 million people may drink well water with dangerously high levels.
Some regions carry a higher risk. The USGS names the Southwest basin fill aquifers, the glacial aquifers of the northern states, the crystalline rock aquifers of the Piedmont and Blue Ridge, and parts of the Mississippi Embayment and Texas Coastal Uplands.
Two wells on the same road can test very differently. A neighbor’s clean result tells you little about your own well.
Arsenic III vs Arsenic V
Arsenic shows up in two main forms. Arsenic III (arsenite) is more common in groundwater and harder to remove, while arsenic V (arsenate) sticks to treatment media far more easily.
This matters when you choose treatment. If your lab can run a speciation test, it tells you which form you have, and that decides whether you need an oxidizing step first.
How to Remove Arsenic From Well Water
| Method | Where it goes | Works on | Watch out for |
|---|---|---|---|
| Reverse osmosis | Kitchen tap | About 95 to 98% of arsenic V, 60 to 65% of arsenic III | Wastes about 3 to 4 gallons per gallon made |
| Metal oxide adsorption filter | One tap or whole house | Both forms, best with pre oxidation | pH and other minerals affect media life |
| Anion exchange | Whole house | Arsenic V only | Sulfate, nitrate and TDS reduce efficiency |
| Activated alumina | One tap or whole house | Arsenic V | Media needs replacing every 1 to 2 years |
| Iron filter (oxidation) | Whole house | Some arsenic along with iron | Removal varies, so test after |
For most homes, a point of use reverse osmosis unit at the kitchen sink is enough, because arsenic is mainly a risk when you drink it. Compare models in my guide to the best under sink reverse osmosis systems for well water.
If you also have iron, fix that first, since iron and arsenic often show up together. My guide on how to remove iron from well water covers the options, and an oxidizing iron filter can take out some arsenic at the same time.
Whatever you fit, test the treated water. Connecticut health officials advise testing treated water at least once a year and more often in the first year.
Testing Your Well for Arsenic
- Use a state certified lab. Penn State Extension puts the cost at about $15 to $50.
- Ask for total arsenic, and speciation if the lab offers it.
- Test when you buy a home, after drilling a new well and at least once if you never have.
- Retest every 5 years if arsenic was detected, and yearly after treatment.
Home test strips can flag a problem, but a lab number is what you need before you spend money on treatment. You can browse arsenic test kits on Amazon or see my picks of the best well water test kits.
Frequently Asked Questions
What level of arsenic in well water is safe?
The EPA limit for public water is 10 parts per billion (0.010 mg/L), and health agencies use the same number for private wells. Lower is better, and New Jersey uses a stricter 5 ppb standard.
Does boiling well water remove arsenic?
No. Boiling does not remove arsenic, and the Virginia Department of Health notes the level can rise slightly as water boils off.
Is it safe to shower in water with arsenic?
Arsenic is mainly a concern when you swallow it, not through skin contact, which is why a single tap system for drinking and cooking water is usually enough. Ask your health department if your level is very high.
Does a water softener remove arsenic?
A standard softener is not designed for arsenic. Anion exchange, which uses a similar tank with a different resin, removes arsenic V but not arsenic III.
How much does an arsenic test cost?
Penn State Extension puts a lab arsenic test at about $15 to $50. Use a state certified lab and ask whether it can also tell you arsenic III from arsenic V.
How often should I test my well for arsenic?
Test at least once, and again when you buy a home or drill a new well. Connecticut advises retesting every 5 years if arsenic is detected, and at least once a year after you install treatment.
Sources: USGS, Arsenic and drinking water; Penn State Extension, Removal of arsenic from wells; Connecticut Department of Public Health, Arsenic in private well water; Virginia Department of Health, Arsenic in private wells.
