Arsenic in private wells: testing and treatment options

Arsenic in private well water is a real concern because you usually cannot see it, smell it, or taste it. The safest way to know whether your household is exposed is to test your water with a state-certified lab, and if the result is at or above the drinking water standard of 10 micrograms per liter, or 10 parts per billion, move quickly to confirm the result and choose a treatment option made to reduce arsenic. (extension.psu.edu)

Boiling does not remove arsenic and can slightly increase the concentration as water evaporates. For most homes, the practical path is simple: test, read the result carefully, install the right treatment if needed, and retest to make sure it is working. (stacks.cdc.gov)

Why arsenic shows up in private wells

Arsenic can get into groundwater from natural deposits in rock, soil, and aquifer minerals. In some places it can also be linked to mining, industrial activity, deep brines from oil and gas development, or older pesticide uses, but natural geology is a common reason it appears in well water. (extension.psu.edu)

This is one reason private wells need their own testing plan. Federal drinking water rules apply to public water systems, but not to privately owned household wells, so the owner is responsible for testing and follow-up. (cdc.gov)

Arsenic is especially tricky because it is invisible in everyday use. Water can look clear and taste normal and still have a level that needs action. Long-term exposure to inorganic arsenic in drinking water has been linked to several cancers, and short-term or higher exposures can cause stomach upset and other symptoms. (stacks.cdc.gov)

When to test your well for arsenic

CDC says every private well owner should test at least once a year for total coliform bacteria, nitrates, total dissolved solids, and pH, and should ask the local health department what other chemicals are important where they live. Arsenic is one of the chemicals CDC specifically says well owners may need to test for, depending on location and local concerns. (cdc.gov)

A good checklist is:

1. Do your routine yearly well test for total coliform bacteria, nitrates, total dissolved solids, and pH. (cdc.gov)
2. Ask your lab or local health department whether arsenic should be added for your area, especially if local geology, mining, drilling, or past results suggest a risk. (cdc.gov)
3. Test sooner if your area has known groundwater problems, your well has been flooded, nearby land use has changed, part of the well system was repaired, or your water suddenly changes in taste, color, or odor. (cdc.gov)
4. Use a state-certified laboratory, not just a quick screening product, when you need a result you can rely on for health decisions or treatment shopping. (cdc.gov)

If you want help building a schedule, start with the Well water test planner. You can also look up certified labs in the state-by-state directory. Rules for private wells, real estate deals, and local response steps can vary by state and sometimes by county or town, so confirm current requirements with your health department, environmental agency, or drinking water office. (cdc.gov)

How to get a useful arsenic test

For arsenic, lab quality matters. CDC recommends using a state-certified laboratory, and EPA says well owners should use labs that are certified for drinking water testing. That gives you a result you can compare to health standards and use when talking with treatment companies. (cdc.gov)

When you order the test, make sure arsenic is actually included on the panel. Then follow the bottle, preservation, and timing instructions exactly. If you need help with the process, these guides can help: How to choose a state-certified drinking water lab and How to collect a well water sample without ruining the test. (cdc.gov)

If you already have a treatment system, do not assume it is still working just because the water looks fine. University of Wisconsin guidance says that if arsenic is detected, you should retest your well each year, and you should test before and after treatment to make sure the device is actually reducing arsenic. (green.extension.wisc.edu)

What your lab result means

The drinking water standard used for arsenic is 10 micrograms per liter, which is the same as 10 parts per billion, or 0.010 milligrams per liter. That number is the maximum contaminant level used for public drinking water systems, and it is the reference point many labs use on private well reports too. (extension.psu.edu)

If your report shows arsenic at or above 10, do not ignore it. EPA says to contact your public health department for specific next steps and to retest to confirm the contaminant and concentration. Penn State notes that well owners with arsenic at or above the standard may need an appropriate treatment device or, if available, a different water source such as a nearby public supply. (epa.gov)

If your result is below 10, that is better, but it is not a lifetime guarantee. Groundwater conditions can change, and arsenic has no warning taste or smell. Keep up your routine testing and ask whether arsenic should stay on your schedule. When arsenic has been found before, yearly retesting is a sensible step and is specifically recommended in University of Wisconsin guidance. (green.extension.wisc.edu)

One more detail can matter: arsenic is not always present in the same chemical form. Penn State notes that arsenite is harder to remove than arsenate, and some treatment setups work better after oxidation changes arsenic into the easier-to-remove form. That is one reason a treatment recommendation should be based on your actual lab report, not on guesswork or a one-size-fits-all sales pitch. For help reading the report itself, see How to read a water test report: MCLs, units and flags. (extension.psu.edu)

Treatment options that can work

The main point to know is that not every filter removes arsenic. CDC says reverse osmosis systems may reduce arsenic, and distillation removes arsenic. University guidance also lists anion exchange and activated alumina as treatment methods used for arsenic, while noting that the best choice depends on the chemistry of your water. (cdc.gov)

Reverse osmosis is a common point-of-use option for drinking and cooking water, often installed at a kitchen sink. It can work well, but CDC says to check the label for the specific chemicals a model removes because reduction claims vary by product. (cdc.gov)

Distillation can also remove arsenic. The tradeoff, according to CDC, is that distillation usually uses more energy and takes longer than other home treatment methods. (cdc.gov)

Activated alumina and anion exchange are other established choices, especially when a professional is matching equipment to your water chemistry. Penn State notes that large point-of-entry devices can treat all household water, while smaller point-of-use systems can treat a single tap. The same source also notes that high total dissolved solids or sulfate can affect which option makes the most sense. (extension.psu.edu)

Whatever device you consider, look for independent certification and read the contaminant claim closely. CDC advises checking the filter label for NSF certification and for what the unit is specifically certified to remove. A unit that improves taste or odor is not automatically an arsenic treatment unit. (cdc.gov)

Just as important, do not rely on the wrong fix. Boiling water will not remove arsenic and may slightly increase its concentration. Ultraviolet systems disinfect water but do not remove chemicals, and ordinary disinfection steps for bacteria problems do not solve dissolved arsenic. (stacks.cdc.gov)

After treatment: maintenance and retesting

An arsenic treatment system is not a set-it-and-forget-it appliance. University of Wisconsin guidance recommends testing before and after treatment and retesting yearly when arsenic has been detected. CDC also says to check a treatment unit’s label and manufacturer information for the contaminants removed and for maintenance needs. (green.extension.wisc.edu)

That means keeping records of the model, replacement parts, service dates, and follow-up lab results. If a cartridge, membrane, or media bed is past its service life, the system may stop working even though water flow looks normal. If your home water chemistry changes, or if treatment equipment starts wearing out quickly, ask whether more testing is needed. (epa.gov)

If your household is also dealing with other well issues such as bacteria, nitrate, lead, or PFAS, make sure the treatment plan covers those too. One device rarely solves every water problem, and some combinations need careful design by a qualified pro using certified lab data. (cdc.gov)

Frequently asked questions

Can I boil water to remove arsenic?

No. CDC says boiling will not remove arsenic and may slightly increase the concentration if enough water boils away as steam. (stacks.cdc.gov)

Is a basic pitcher or taste-and-odor filter enough?

Not necessarily. CDC says to check the label for independent certification and for the exact contaminants the device reduces. A filter that helps with taste, odor, or chlorine is not automatically certified to reduce arsenic. (cdc.gov)

Do I need a whole-house system or just a kitchen sink unit?

It depends on your water chemistry and household needs. Penn State notes that some homes use smaller point-of-use treatment at one tap, while others use point-of-entry treatment for the whole house. The right choice depends on the lab result, the form of arsenic present, and any other contaminants that may affect treatment. (extension.psu.edu)

If my arsenic result is under 10 ppb, should I test again later?

Yes. CDC recommends yearly private well testing for core items and says to ask about other chemicals, including arsenic, based on where you live. University of Wisconsin guidance adds that if arsenic has been detected, yearly retesting is recommended. (cdc.gov)