How common is arsenic in well water?

More common than most people expect. A USGS model estimates approximately 2.1 million people in the US drink domestic well water with arsenic above the EPA limit of 10 ppb. In some bedrock regions of New England, up to 30% of private wells exceed that limit. If you're on a private well and have never tested for arsenic specifically, you don't know your level.

What does arsenic in water do to your health?

Long-term exposure above the EPA limit is linked to bladder, lung, kidney, and liver cancers. It's also associated with cardiovascular disease and diabetes. The EPA's Maximum Contaminant Level Goal (MCLG) for arsenic is zero, meaning the agency acknowledges no safe level exists. The enforceable limit of 10 ppb is set at the point where treatment is technically and economically feasible for public systems, not at a level the EPA considers risk-free.

Does reverse osmosis remove arsenic?

Yes. A reverse osmosis system certified to NSF/ANSI 58 removes arsenic to below detectable levels in most cases. It's the most practical point-of-use solution for arsenic in drinking water. Activated alumina filters also remove arsenic effectively. Standard carbon filters, water softeners, and boiling do not.

How do I test my well water for arsenic?

Use a certified lab test, not a home strip. Home test strips aren't reliable at the levels that matter for arsenic. A dedicated arsenic lab test typically costs $15 to $50. Some state health departments in Maine, New Hampshire, Arizona, and Nevada offer subsidized testing for well owners. Contact your state's drinking water program to ask.

Is arsenic in well water an emergency?

Not in the immediate, acute sense. Arsenic risk comes from long-term exposure, not a single glass of water. That said, don't delay testing if you're in a high-risk region and have never checked. The longer you wait, the longer exposure continues. If you get a result above 10 ppb, stop using that water for drinking and cooking until you have a treatment plan.

Arsenic in Well Water: Risk by Region and What to Do

Health disclaimer: Arsenic exposure is a serious long-term health risk. This page provides general information, not medical advice. If you have concerns about arsenic exposure, talk to your doctor or local health department.

About 2.1 million people in the US drink well water with arsenic above the EPA’s limit of 10 parts per billion. That’s a USGS model estimate. Most of them have no idea.

You can’t see arsenic. You can’t smell it. You can’t taste it at the concentrations that cause harm. The only way to know your level is to test.

Where Arsenic Is Most Common

Arsenic in groundwater comes from natural rock formations, not pollution. Certain geologic regions have bedrock or aquifer sediments with high arsenic content. When water moves through those formations, it picks up arsenic. The USGS has mapped this extensively in their arsenic and drinking water research.

New England has some of the highest rates in the country. Maine and New Hampshire stand out. In certain bedrock areas, up to 30% of private wells exceed the 10 ppb limit. The source is metasedimentary bedrock, a type of rock that formed from marine sediments and contains naturally elevated arsenic. It’s widespread across both states and extends into parts of Vermont and Massachusetts.

The Southwest is another high-risk zone. Arizona, Nevada, southern California, and parts of Texas sit over basin-fill aquifers where arsenic concentrations are naturally high. USGS data shows roughly 16% of sampled wells in this region exceed the MCL, about double the national rate.

The Upper Midwest also has pockets of concern. Parts of Minnesota and Michigan have elevated arsenic in private wells, tied to specific glacial sediment deposits and bedrock formations.

If you’re in a lower-risk area, that doesn’t mean your well is clean. It means the odds are lower. Arsenic can appear in isolated pockets anywhere. The only way to rule it out is a test.

The Regulation Gap

Public water systems must test for arsenic regularly. If a system exceeds 10 ppb, it has to treat the water or notify customers and take corrective action. That rule has been in place since the EPA lowered the limit from 50 ppb to 10 ppb in 2001.

Private wells are different. No federal agency tests your private well. No utility monitors it. State programs vary widely in what they require or offer. You’re responsible for knowing what’s in your water.

That’s not a criticism of any agency. It’s just how the system works. Public water: regulated. Private well: your call.

Health Effects

The EPA’s Maximum Contaminant Level Goal for arsenic is zero. The MCLG is the health-based target, the level at which no known risk exists. A goal of zero means the agency has concluded there’s no threshold below which arsenic is definitively safe.

The enforceable limit of 10 ppb exists because the EPA must balance risk against what’s technically and economically achievable. It’s not a safe level. It’s the best achievable level for public systems.

Long-term exposure above 10 ppb is linked to bladder cancer, lung cancer, kidney cancer, and liver cancer. It’s also associated with cardiovascular disease and type 2 diabetes. These are chronic risks from years of regular exposure, not short-term effects from a single exposure event.

Children and pregnant people face the greatest risk from long-term arsenic exposure, though the research on arsenic is less age-specific than with lead. The core concern is cumulative dose over time.

Testing Your Well

A certified lab test is the right tool here. Home arsenic test strips exist, but they’re not reliable at the concentrations that matter. A strip might detect 50 ppb but miss 12 ppb, and 12 ppb is above the EPA limit. You need a lab.

An arsenic-specific test from a state-certified lab typically costs $15 to $50. Some full water panels include arsenic. If you haven’t tested for anything, a broader well water panel makes sense. But arsenic should be on the list explicitly.

Several high-risk states offer subsidized or free arsenic testing for private well owners. Maine’s CDC and New Hampshire’s Department of Environmental Services have both run testing programs. Arizona and Nevada have also offered assistance through local health departments. Contact your state’s drinking water program directly to find out what’s currently available.

The USGS recommends testing any private well in a high-risk region at least once, even if your water looks and tastes fine. For deeper detail on what to test and when, see the well water testing guide.

For lab test options, the best mail-in water tests page covers certified labs that handle arsenic specifically.

What Removes Arsenic

The short list of what works:

Reverse osmosis (NSF/ANSI 58 certified). An RO system at your kitchen sink removes arsenic to below detectable levels in most cases. This is the most practical solution for most families. It’s relatively affordable to install under a sink, and it handles arsenic alongside other dissolved contaminants. The best under-sink RO systems covers certified options.

Activated alumina. This filter media binds arsenic directly. Some whole-house systems use it. Point-of-use activated alumina systems are also available. It’s specifically designed for arsenic and fluoride removal.

Ion exchange. Certain ion exchange resins remove arsenic at point-of-use. Less common than RO for household use, but effective.

What doesn’t work: standard carbon block filters, pitcher filters without arsenic-specific certification, water softeners, and boiling. Boiling concentrates arsenic, just like it concentrates lead. Never boil water as a treatment for arsenic.

Whole-House vs. Point-of-Use

This question comes up often. The short answer: point-of-use is usually enough.

Unlike bacteria or volatile organic compounds, arsenic doesn’t absorb meaningfully through skin during showering. The health risk is from ingestion, which means drinking water and food cooked in water. If you treat your kitchen tap with an under-sink RO system, you’ve addressed the primary exposure pathway.

Whole-house arsenic removal exists. Activated alumina tanks can treat water at the point of entry before it reaches any tap. But whole-house systems for arsenic are expensive to buy and maintain. For most families on a private well, an under-sink RO at the kitchen tap is the practical first step.

If you have infants or young children who bathe in the water, and your arsenic level is significantly above 10 ppb, talk to a water treatment professional about whole-house options. That’s a case where the calculus shifts.

The Direct Recommendation

If you’re in Maine, New Hampshire, Arizona, Nevada, or rural parts of the Midwest and Southwest, and you’re on a private well, test for arsenic. Get a certified lab test. It costs less than $50. Most results come back within a week.

If your level is below 10 ppb, you have useful information and you can stop worrying. If it’s above 10 ppb, you have a clear path: an under-sink RO system resolves the drinking and cooking exposure. The how-to guide on removing arsenic from water walks through your options based on your test result.

Not knowing is the only outcome with no good answer.

Health disclaimer: WaterAnswer.com provides general information only. For health concerns related to arsenic exposure, contact your doctor or your local or state health department.