Arsenic in Well Water: Testing and Removal Options
Arsenic in Well Water: Testing and Removal Options
By the WellWater HQ team
The EPA’s enforceable limit for arsenic in drinking water is 0.010 mg/L (10 parts per billion), a standard set in 2001 and phased in for public systems by 2006, replacing the older 50 ppb limit (EPA, Drinking Water Arsenic Rule History, 2026). Private wells aren’t legally bound by that number, but it’s the threshold every certified lab, health department, and toxicologist uses to judge a well’s result.
Arsenic is colorless, odorless, and tasteless, so there’s no sensory warning sign; testing is the only way to know it’s there. It occurs naturally in groundwater from bedrock in many parts of the country, especially New England, the upper Midwest, and parts of the Southwest, which means a well can carry elevated arsenic even with no nearby industrial or agricultural source.
What are the health risks of arsenic in well water?
Long-term exposure to arsenic above the EPA’s limit is linked to skin, bladder, and lung cancers, along with cardiovascular disease and developmental effects in children, based on decades of epidemiological research the EPA’s 2001 rulemaking relied on (Federal Register, National Primary Drinking Water Regulations: Arsenic, 2001). The International Agency for Research on Cancer classifies arsenic as a Group 1 human carcinogen, the agency’s highest-certainty category.
These are long-term, cumulative-exposure risks tied to years of drinking water above the limit, not a symptom you’d notice after a single glass. That’s exactly why testing matters more than watching for signs: there aren’t any until the exposure has already been sustained.
Is arsenic part of the standard annual well water test?
No, and this is a common gap in what homeowners assume they’ve covered. The EPA’s core annual testing recommendation for private wells covers total coliform bacteria, nitrate, total dissolved solids, and pH; arsenic falls under the broader panel the EPA recommends every 3 to 5 years, or sooner in regions with known geologic risk (EPA, Protect Your Home’s Water, 2026). A homeowner who’s diligent about the annual test can still have never actually tested for arsenic unless they specifically ordered it.
Check with your state health department or geological survey for local arsenic risk maps; some states, particularly in New England, publish well-by-well or township-level data showing where arsenic is most commonly found in groundwater.
Why does arsenic’s chemical form matter for removal?
Arsenic occurs in water in two oxidation states: arsenite (arsenic III), which carries no electrical charge, and arsenate (arsenic V), which does. Most removal technologies, including reverse osmosis and standard anion exchange resin, rely on that charge to capture arsenic, which means they remove arsenate far more completely than arsenite.
Reverse osmosis alone typically removes 60 to 80 percent of arsenic III, but adding a pre-oxidation step, commonly a small chlorine dose, to convert arsenic III into arsenate before it hits the membrane pushes removal to 95 to 99 percent (ScienceDirect, Removal of arsenic as a potentially toxic element from drinking water by filtration, 2023). A certified lab that reports arsenic speciation, not just a total arsenic number, tells you whether your well needs that extra oxidation step.
What removes arsenic from well water?
| Method | How it works | Notes |
|---|---|---|
| Reverse osmosis (NSF/ANSI 58) | Membrane blocks charged arsenate ions; arsenite passes more easily | Pair with pre-oxidation if arsenic III is present |
| Anion exchange | Resin swaps arsenate ions for chloride | Also charge-dependent; needs oxidized arsenic to work fully |
| Adsorptive media (activated alumina, iron-based) | Arsenic binds to the media’s surface | Point-of-use cartridges available; media needs periodic replacement |
| Distillation | Boils water, collects only the condensed vapor | Effective on both arsenic forms, but slow and impractical whole-house |
Reverse osmosis and adsorptive media are usually installed at a single kitchen tap, since arsenic exposure that matters is what you drink and cook with, not what you shower in. Whole-house arsenic treatment exists but costs considerably more and is uncommon for residential wells.
How much does arsenic testing and removal cost?
A certified lab arsenic test typically runs $15 to $50 as an add-on to a broader well panel, or somewhat more as a standalone test depending on the lab. Point-of-use treatment, an under-sink RO or adsorptive media system, runs $150 to $1,200 in equipment plus installation, with ongoing media or cartridge replacement costs that vary by how much arsenic the system is removing and how much water runs through it.
Contact your state health department before paying for private lab testing; some offer free or reduced-cost arsenic screening, particularly in counties with known elevated groundwater arsenic.
How is arsenic tested, and how often?
A certified laboratory test that reports both total arsenic and speciation (arsenic III versus arsenic V) gives you the number to compare against the EPA’s 0.010 mg/L limit and tells you which removal method will actually work. Test as part of your broader well panel every 3 to 5 years, or sooner if you’re in a region with known geologic arsenic risk, and retest after installing any removal system to confirm it’s performing as expected.
Run your lab report through the WellWater HQ test result checker to see whether your arsenic level and its chemical form point toward RO, anion exchange, or adsorptive media. The WellWater HQ well water handbook covers the full contaminant panel and testing calendar the EPA recommends for private wells.
FAQ
What level of arsenic in well water is considered unsafe? The EPA’s enforceable limit for public water systems is 0.010 mg/L (10 ppb). Private wells aren’t legally bound by it, but it’s the number labs and health departments use to judge whether a result needs treatment.
Can you taste or smell arsenic in water? No. Arsenic is colorless, odorless, and tasteless at the concentrations found in groundwater, which is why testing is the only reliable way to detect it.
Does a standard well water test include arsenic? Not usually. The EPA’s core annual test panel covers coliform bacteria, nitrate, TDS, and pH; arsenic is part of the broader panel recommended every 3 to 5 years and has to be ordered specifically.
What removes arsenic from well water? Reverse osmosis, anion exchange, and adsorptive media like activated alumina are the main effective methods. Effectiveness depends on the arsenic’s chemical form; arsenic III often needs a pre-oxidation step to remove as completely as arsenic V.
How much does it cost to remove arsenic from well water? Point-of-use systems run $150 to $1,200 installed, plus ongoing media or membrane replacement. Whole-house arsenic treatment is far more expensive and uncommon for residential wells; most households treat only their drinking-water tap.
Bottom line: arsenic is invisible and isn’t covered by a standard annual well test, so it has to be ordered specifically. Once you know your level and its chemical form, reverse osmosis, anion exchange, or adsorptive media all bring it below the EPA’s limit at a single tap.