Arsenic in Drinking Water: Health Risks, Testing, and How to Remove It

LAST UPDATED: July 2026

Arsenic is a naturally occurring element, classified as a Group 1 human carcinogen by the International Agency for Research on Cancer, that contaminates groundwater in much of the United States — particularly the desert Southwest, the Great Plains, and parts of New England. The EPA’s enforceable limit is 10 parts per billion (ppb), and the household technologies verified to reduce arsenic are reverse osmosis and specialized adsorption media certified to NSF/ANSI 58 or 53 — not standard carbon pitchers, and not boiling.

Arsenic is different from most contaminants this site covers in one important way: it usually has nothing to do with industrial pollution or failing pipes. It leaches into groundwater from the rock the water moves through. That means a pristine-looking rural well can carry more arsenic than a city tap, and it means the problem does not go away when the water “looks fine.” Arsenic is colorless, tasteless, and odorless at the concentrations found in drinking water. Testing is the only way to know it is there.

KEY TAKEAWAYS

Arsenic is a Group 1 human carcinogen (IARC’s highest classification) linked to bladder, lung, and skin cancers with long-term exposure.
The EPA’s maximum contaminant level is 10 ppb, in effect since 2006. The health-based goal (MCLG) is zero, and New Jersey and New Hampshire enforce a stricter 5 ppb.
Private wells are the highest-risk scenario. The Safe Drinking Water Act does not cover them, and a USGS analysis estimated roughly 2.1 million Americans use domestic wells with arsenic above 10 ppb.
Reverse osmosis certified to NSF/ANSI 58 for arsenic reduction is the most practical household removal method. Boiling water concentrates arsenic rather than removing it.
Arsenic exists in two forms — arsenite, As(III), and arsenate, As(V) — and most certified treatment performs best against As(V). Well owners may need oxidation pretreatment. The distinction matters.

What Arsenic Is and How It Gets Into Drinking Water

Arsenic is a metalloid (an element with properties between metals and nonmetals) that occurs naturally in rock, soil, and minerals. As groundwater moves through arsenic-bearing formations, it dissolves trace amounts of the element. Concentration depends almost entirely on local geology: two wells a mile apart can test at 2 ppb and 40 ppb.

Geogenic arsenic — the naturally occurring kind — is the dominant source in US drinking water. It is most prevalent in the Southwest (Arizona, New Mexico, Nevada, parts of California and Texas), the upper Midwest and Great Plains, and portions of New England, where glacial and bedrock aquifers carry it. This is why arsenic appears repeatedly in our city water reports for Phoenix, Tucson, Albuquerque, El Paso, and Fresno — the desert cluster draws on groundwater that moves through exactly this kind of geology.

Human activity adds to the load in specific places. Arsenical pesticides were used on orchards and cotton fields for decades before being phased out, and that legacy arsenic persists in soil. Mining and smelting operations mobilize it. Wood treated with chromated copper arsenate (CCA), common in decks and playgrounds before the 2003 residential phase-out, can leach arsenic locally. But if your water has arsenic in it, the most likely explanation is the rock underneath you, not a polluter upstream.

The Two Forms: Arsenite and Arsenate

Dissolved arsenic occurs in two oxidation states, and the difference determines how well treatment works.

Arsenate, As(V), is the oxidized form that dominates in chlorinated municipal water and oxygen-rich groundwater. It carries a charge in water, which makes it comparatively easy to capture with reverse osmosis membranes and adsorption media.

Arsenite, As(III), dominates in deeper, oxygen-poor groundwater — which is to say, in many private wells. It is both more toxic and harder to remove; it passes through some treatment that captures As(V) reliably. Converting As(III) to As(V) with an oxidant (chlorine, or an oxidizing media bed) is standard pretreatment in well systems where arsenite is present.

The practical consequence: a certified filter’s arsenic claim is typically tested against pentavalent arsenic, As(V). On chlorinated city water, that matches what is in your glass. On a private well, a lab test that speciates the arsenic (reports the two forms separately) tells you whether you need oxidation ahead of the filter.

Health Effects: What the Research Shows

Arsenic’s toxicity is not in dispute. It is one of the most thoroughly studied drinking-water contaminants in the world, largely because of mass-exposure events in Bangladesh, Taiwan, and Chile that gave epidemiologists decades of dose-response data.

Cancer

IARC classifies arsenic and inorganic arsenic compounds as Group 1 — carcinogenic to humans, its highest-confidence category. Chronic ingestion is most strongly associated with cancers of the bladder, lungs, and skin, with evidence also linking it to kidney and liver cancers. The 2001 National Research Council review that preceded the current EPA rule concluded that the cancer risk at the then-legal limit of 50 ppb was far higher than the EPA typically tolerates for a regulated contaminant — which is what drove the standard down to 10 ppb.

Non-Cancer Effects

Long-term exposure below acutely toxic levels is associated with skin changes (hyperpigmentation and keratoses — thickened, wart-like patches on palms and soles that are a classic clinical sign of arsenic exposure), cardiovascular disease, and type 2 diabetes. Research on prenatal and early-childhood exposure associates arsenic with reduced cognitive development, which is why households with infants — particularly those mixing formula with well water — have the least margin for error.

Two points of context keep the risk proportionate. First, these effects are driven by chronic exposure over years, not by a single glass of water at 15 ppb. Second, risk scales with dose: the difference between 8 ppb and 60 ppb is substantial. The goal is not panic at any detection — it is knowing your number and acting on it.

What the Regulations Do and Do Not Cover

The EPA set the current arsenic MCL of 10 ppb in 2001, with compliance required by 2006. It replaced a 50 ppb standard that had stood since 1942 — before arsenic’s carcinogenicity in drinking water was established. The maximum contaminant level goal, the level at which the EPA expects no adverse health effects, is zero. The 10 ppb enforceable standard reflects treatment cost and feasibility, not a threshold below which arsenic is harmless. The World Health Organization’s guideline value is the same 10 µg/L, with the same caveat attached.

Two states have concluded 10 ppb is not protective enough: New Jersey and New Hampshire both enforce 5 ppb for public water systems.

The exposure picture splits along a single line — who is responsible for testing the water. Public water systems must test for arsenic and report it in their annual Consumer Confidence Reports, and most large systems comply with the MCL — though compliance has historically been weakest among small groundwater-dependent systems in the Southwest, where treatment costs fall on a few thousand ratepayers. Private wells are another matter entirely. The Safe Drinking Water Act does not regulate them; no one tests a private well unless the owner does. A US Geological Survey analysis (Ayotte et al., 2017) estimated that about 2.1 million people in the US draw water from domestic wells with arsenic concentrations above 10 ppb — most of them unaware, because nothing about the water signals a problem.

If you are on a well, our well water testing guide covers the full testing workflow; arsenic should be on the panel every time.

How to Test Your Water for Arsenic

Because arsenic has no taste, odor, or color, testing is not optional — it is the entire diagnostic step.

On municipal water: start with your utility’s Consumer Confidence Report, which lists detected arsenic and the system’s compliance status. The limitation is that the CCR reports system-wide sampling, not your tap, and levels in groundwater-blended systems can vary by neighborhood and season.

For your specific tap, use a certified laboratory. A mail-in lab panel such as Tap Score reports arsenic down to sub-ppb levels and — importantly for well owners — offers speciation between As(III) and As(V), which determines treatment design. State-certified local labs are an equivalent option; many state health departments subsidize arsenic tests for well owners in high-risk counties.

Home test strips for arsenic exist and are inexpensive, but they are semi-quantitative — they bracket a concentration range rather than measure it. They are reasonable as a screening step; they are not a basis for choosing (or skipping) a treatment system. Our guide to testing your water at home covers where strips fit and where they do not.

Which Water Filters Remove Arsenic?

Most filters do not. Arsenic is dissolved and inorganic, so the activated carbon that handles chlorine, taste, and many organic contaminants does very little against it on its own. A standard carbon pitcher, a basic faucet filter, a water softener, and boiling all fail here — boiling actually increases the arsenic concentration as water evaporates. That claim requires context whenever a filter’s marketing says “reduces 1,000+ contaminants”: unless the product holds a certification specifically listing arsenic, assume it does not remove it.

What the Certifications Mean

Arsenic reduction claims are certified under NSF/ANSI 58 (reverse osmosis systems) and NSF/ANSI 53 (adsorption-based filters with arsenic-specific media). Certification is issued by one of three ANSI-accredited bodies — NSF International, WQA Gold Seal, or IAPMO R&T — and the certified claim is typically for pentavalent arsenic, As(V). “Tested to NSF standards” is a one-time lab claim, not certification, and NSF/ANSI 372 covers lead-free materials only — neither is evidence a product removes arsenic. Verify the listing in the certifier’s own database — NSF’s certified products directory — before you buy.

Reverse Osmosis (the practical default)

Reverse osmosis (a membrane process that rejects dissolved contaminants at the molecular level) is the most accessible certified option for a household tap, and it is the technology our reverse osmosis buying guide covers in depth. Certified performers for arsenic include:

AquaTru Classic countertop RO — certified by IAPMO R&T to NSF/ANSI 42, 53, 58, and 401, with arsenic among its certified reduction claims (alongside lead, chromium-6, fluoride, and PFOA/PFOS). Because it is a countertop unit requiring no plumbing, it is the realistic option for renters on arsenic-affected water. Check on Amazon
Pentair FreshPoint GRO-575B under-sink RO — certified by NSF International to NSF/ANSI 42, 53, and 58 with arsenic in its certified claim set (along with lead, chromium-6, and fluoride). Sold through Pentair and plumbing retailers.

An RO system’s arsenic certification applies to As(V); on a well with significant As(III), pair it with oxidation pretreatment per your lab’s speciation results.

Adsorption Filters Certified Under NSF/ANSI 53

A small number of non-RO filters carry a genuine arsenic certification by using arsenic-selective media. The clearest example is the MultiPure Aquaperform (MP880), a carbon-block under-sink unit certified by NSF International to NSF/ANSI 42, 53, and 401, with arsenic V in its certified NSF/ANSI 53 claims along with lead and PFOA/PFOS. MultiPure sells through a distributor network and we have no affiliate relationship with the company — it is listed here because the certification is in NSF’s own database, which is the only criterion that matters.

Whole-House and Well Systems

Point-of-entry arsenic treatment for wells — oxidation followed by iron-based adsorption media or anion exchange — is effective but is engineering, not an off-the-shelf purchase. Media selection depends on arsenic speciation, pH, iron, and silica levels in your specific water. Get the lab report first, then size the system to it; a well professional or your state’s rural water association can spec this. For context on how well treatment trains fit together, see our well water filtration guide.

What to Do, In Order

Test. CCR first if you are on city water; a certified lab panel with arsenic speciation if you are on a well.
Interpret against 10 ppb — and against zero. Above 10 ppb warrants treatment without debate. Between detection and 10 ppb, treatment is a reasonable precaution given the MCLG of zero, particularly for households with young children.
Match treatment to the result. Certified RO or an NSF/ANSI 53 arsenic-certified filter at the kitchen tap for drinking and cooking water; whole-house treatment generally only makes sense for wells with high concentrations.
Retest after installation and on the filter’s replacement schedule. Certified performance assumes maintained media — an exhausted cartridge removes nothing.

Frequently Asked Questions

Does boiling water remove arsenic?

No. Boiling removes microorganisms, not dissolved elements. Because some water evaporates during boiling, the arsenic that remains becomes slightly more concentrated. The same is true of letting water stand. Removal requires a physical treatment barrier — certified reverse osmosis or arsenic-specific adsorption media.

Do Brita or other pitcher filters remove arsenic?

No standard carbon pitcher carries an arsenic certification, including Brita’s. Pitcher filters are certified (at best) for contaminants like chlorine, lead, or PFAS — check each model’s actual certified claim list. For arsenic, the certified household options are reverse osmosis systems under NSF/ANSI 58 or adsorption filters with arsenic listed under NSF/ANSI 53.

What level of arsenic in water is safe?

The EPA’s enforceable limit is 10 ppb, but its health-based goal is zero, and IARC classifies arsenic as a known human carcinogen with no established safe threshold for cancer risk. Risk scales with concentration and duration of exposure. Treat anything above 10 ppb as requiring action, and regard levels below that as a judgment call weighted by who in the household drinks the water.

Does a water softener remove arsenic?

No. Softeners exchange calcium and magnesium for sodium; they are not designed to capture arsenic and are not certified for it. If a well needs both hardness and arsenic treatment, the arsenic stage is a separate component in the treatment train.

How do I find out if my well has arsenic?

Order a certified lab test — arsenic is inexpensive to add to any well panel, and speciated tests report As(III) and As(V) separately, which determines what treatment will work. Many state health departments maintain arsenic risk maps and subsidize testing in high-risk areas. Retest every one to two years; arsenic levels in wells can shift with drawdown and seasonal water-table changes.

Sources Cited

EPA — National Primary Drinking Water Regulations, arsenic MCL 10 ppb / MCLG zero (Arsenic Rule, 66 FR 6976, January 2001; compliance 2006)
International Agency for Research on Cancer — Monographs, arsenic and inorganic arsenic compounds (Group 1)
National Research Council — Arsenic in Drinking Water: 2001 Update
US Geological Survey — Ayotte et al., “Estimating the High-Arsenic Domestic-Well Population in the Conterminous United States,” Environmental Science & Technology (2017)
World Health Organization — Guidelines for Drinking-water Quality, arsenic (10 µg/L)
NSF International — certified product listings — MultiPure Aquaperform, Pentair FreshPoint GRO-575B
IAPMO R&T — product listing directory — AquaTru certifications

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