Why it matters
Connecticut Department of Public Health calls arsenic a human carcinogen. Very high concentrations are linked to bladder, lung, liver and skin cancer, and long-term exposure can also cause cardiovascular and skin problems.
The limit of 10 micrograms per liter (0.01 mg/L) is the public-water standard. EPA says private wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments, so testing and treating the water is the owner's job.
Where arsenic in a well comes from
Arsenic is often natural in bedrock and soil: it dissolves into the groundwater. It can also come from human activity, such as old pesticides and wood preservatives. It has no taste, color or smell, so the only way to know is a lab test.
If your result is above the limit
- Boiling does not remove arsenic, and Minnesota Department of Health says it only concentrates it. Use bottled water for drinking and cooking until you treat it.
- Ask your state or local health department what to do next, and whether it has advice for your area.
- Have a water treatment pro pick a system for the form of arsenic in your water, and test the treated water to confirm it works.
How to test
- Use a state-certified lab. Connecticut says testing through one is the only way to know.
- Connecticut advises retesting every 5 years if arsenic is detected. Your state may say otherwise.
What removes it
- Reverse osmosis removes about 60 to 65 percent of arsenic III and 95 to 98 percent of arsenic V, and wastes about 3 to 4 gallons per gallon treated.
- Metal oxide (adsorptive) filters can be at one tap or whole house. Pre-oxidation is advised if arsenic III is present.
- Ion exchange removes arsenic V well but not arsenic III, unless an oxidizer is installed first.
- A total arsenic result combines both forms, so you may need an arsenic III test to choose treatment. Test treated water at least once a year.
Questions
Does boiling remove arsenic from well water?
No. Minnesota Department of Health says boiling only concentrates arsenic, because some of the water evaporates. Use bottled water until the water is treated and the treated water tests clean.
How often should I retest for arsenic?
Connecticut advises retesting every 5 years if arsenic is detected, and testing treated water at least once a year. Your state may say otherwise, so ask your health department.
Which treatment removes arsenic?
Reverse osmosis, metal oxide (adsorptive) filters and ion exchange can remove it. Which one works depends on whether the arsenic is arsenic III or arsenic V, so have a lab test for arsenic III, or put an oxidizer before the filter.
Does a total arsenic result tell me which treatment to buy?
Not by itself. A total result combines both forms, and ion exchange removes arsenic V well but not arsenic III. Have a lab test for arsenic III, or put an oxidizer before the filter to turn arsenic III into arsenic V.
Is the 10 microgram limit a safe level?
It is the enforceable public-water limit. Connecticut calls arsenic a human carcinogen, so treat any detection as a reason to ask your state health department what to do.
Who treats arsenic?
A local water treatment pro can pick a system for your form of arsenic and your water, and should test the treated water to confirm it works.
Next step
- Well water treatment picker: the type of system that fits your results
- Well water test results explained: enter your lab numbers and get a next step