Arsenic is one of the few contaminants where the federal government openly acknowledges that the legal limit in your tap water is not a safe level — it's a balance point between health protection and the cost of treatment.
When the EPA set the 10 parts per billion (ppb) standard in 2001, it estimated that drinking water at exactly 10 ppb over a lifetime would cause approximately 1 in 300 people to develop bladder or lung cancer from that exposure. The EPA accepted this level because the cost of stricter standards would have been prohibitive for thousands of small water systems.
That context matters a great deal for how to think about arsenic in your water.
Where Arsenic in Drinking Water Comes From
Natural geology is the dominant source in the US. Arsenic is present in many rock formations -- particularly the volcanic and sedimentary geology of the western US, the New England granite aquifers, and parts of the Great Plains and Midwest. When groundwater dissolves through arsenic-bearing minerals, it carries arsenic into wells and aquifers that feed municipal systems.
This is why arsenic levels are so much higher in places like Phoenix, Arizona (up to 8.3 ppb in recent testing), rural New Mexico, Nevada, and parts of New England than in cities drawing from surface water sources like the Great Lakes. It's not pollution in the traditional sense -- it's geology.
Industrial sources also contribute in some locations. Arsenic is a byproduct of copper smelting and has been used in pesticides (particularly in orchards -- old apple orchard soils in the Northeast often retain arsenic). Coal combustion byproducts, wood preservatives (CCA-treated lumber was widely used until 2003), and some mining operations have all contributed arsenic to specific local water supplies.
Private wells are not regulated by the EPA and are not required to test for arsenic. Many rural well owners have no idea whether their water contains arsenic, particularly in high-risk geological areas. If you have a private well and have never tested for arsenic, testing is strongly recommended.
The Health Evidence
Arsenic is a Group 1 human carcinogen -- the highest classification from the International Agency for Research on Cancer (IARC), meaning there is sufficient evidence of carcinogenicity in humans. This is not a marginal or disputed finding.
Cancer risks: The most well-established cancers from arsenic in drinking water are bladder cancer (the strongest dose-response relationship in the literature), lung cancer (elevated risk from ingestion, not just inhalation), and skin cancer (including characteristic arsenic-related skin lesions at higher exposures). Secondary associations include kidney, liver, and prostate cancers.
Non-cancer effects: Arsenic exposure is also associated with cardiovascular disease, type 2 diabetes, neurological effects, and adverse reproductive outcomes. Developmental effects in children -- including reduced IQ and cognitive effects -- have been documented in populations with higher arsenic exposures.
The dose makes the poison, but there's no safe dose. Unlike some contaminants where a threshold exists below which no harm occurs, the EPA's Maximum Contaminant Level Goal (MCLG) for arsenic is 0 ppb -- the agency's acknowledgment that no level of arsenic is considered safe. The 10 ppb MCL is an enforceable compromise, not a safety threshold.
Who Is Most At Risk
Private well users in high-arsenic geological areas who have never tested are the highest-risk group. Many wells in New England, the Southwest, Rocky Mountain West, and parts of the Midwest have arsenic above 10 ppb -- often far above.
Phoenix and Southwest residents receiving water from utilities with elevated arsenic (mostly from natural geological sources in the Colorado River watershed and Arizona groundwater) are also at elevated risk. Children and infants face greater developmental exposure risk. People drinking large volumes of water daily have proportionally higher arsenic intake.
People whose water comes from groundwater rather than surface water are most likely to have elevated arsenic. Surface water typically has lower arsenic because runoff dilutes it and treatment processes remove more.
What Your Federal Compliance Data Means (and Doesn't)
When a utility's Consumer Confidence Report says it is "in compliance" with the arsenic MCL, that means arsenic levels are below 10 ppb. It does not mean arsenic is absent, and it does not mean there is no health risk.
A utility reporting 9 ppb arsenic is technically compliant but exposing residents to levels the EPA itself estimated carry a ~1 in 300 lifetime cancer risk.
The EWG health guideline for arsenic is 0.004 ppb -- 2,500 times more stringent than the federal limit. This is a health-based benchmark; utilities are not required to meet it, but it shows how far the regulatory limit is from a "no added risk" threshold.
The practical implication: If your water system reports any detectable arsenic above about 1 ppb, point-of-use filtration for drinking and cooking water is a reasonable precaution. At levels above 5 ppb, it becomes more pressing.
Check your utility's arsenic levels at PureCity -- enter your ZIP to see what your system has reported.
Private Well Testing
If you have a private well in any of these areas, arsenic testing is strongly recommended if you haven't done it recently: Arizona, New Mexico, Nevada, California (particularly inland areas), New England (Maine, New Hampshire, Vermont have among the highest private well arsenic rates in the US), Rocky Mountain states (Montana, Idaho, Wyoming), and parts of the Midwest (Minnesota, Wisconsin, Iowa).
Arsenic is tasteless, colorless, and odorless -- you cannot detect it without a test. The Tap Score Essential Well Water Test covers arsenic alongside bacteria, nitrates, lead, iron, manganese, and 110+ other parameters, with certified lab results and a clear digital report. It's the most comprehensive and clearly reported well water test available. For municipal water users, the Tap Score Essential City Water Test covers arsenic in the context of a full 50+ parameter panel. See our complete water testing guide for more detail. Your county extension office or state health department may also offer free or subsidized testing for well owners.
What Removes Arsenic
The chemistry here is important. Arsenic in drinking water occurs in two forms:
- Arsenate (As V) -- typically present in oxygenated surface water and treated municipal supplies. Easier to remove.
- Arsenite (As III) -- more toxic, present in reducing groundwater conditions (particularly in private wells). Harder to remove; must be oxidized to As V before most removal processes work effectively.
Most home filters assume As V (arsenate). If you have a private well with reducing conditions, testing to confirm the arsenic species is important before relying on any filter.
Reverse osmosis is the most reliable and comprehensive home treatment for arsenic -- removing 94--96% of arsenate and, with proper pretreatment, comparable removal of arsenite. This is EPA's recommended approach for point-of-use arsenic treatment.
What does NOT remove arsenic: Standard activated carbon filters (Brita, PUR, most pitcher filters), water softeners, boiling (which concentrates arsenic), and UV disinfection (which addresses bacteria, not dissolved minerals).
Filters That Remove Arsenic
- ✓NSF 58 certified -- removes arsenic, lead, PFAS, nitrates, fluoride, and DBPs
- ✓WQA Gold Seal; made in USA; proven decade-long track record
- ✓Standard 10-inch filter replacements widely available from multiple suppliers
- ✓~$50-70/year in replacement filters -- low ongoing cost
- Requires one drilled faucet hole and basic under-sink plumbing
- 4:1 waste water ratio
- Not suitable for renters without landlord approval
The benchmark for arsenic removal at home. One system addresses every major drinking water concern simultaneously -- the right choice for Phoenix, Southwest, and New England well water.
- ✓All the arsenic removal of standard RO -- 94-96% rejection
- ✓6th alkaline stage restores minerals after RO strips them -- noticeably better taste
- ✓WQA certified; good for households who find flat RO water unappealing
- ✓Transparent filter housings for easy monitoring
- Slightly larger footprint than the APEC
- Higher price than the APEC ROES-50
- 4:1 waste water ratio
The upgrade pick if you want better-tasting drinking water alongside comprehensive arsenic removal. The remineralization stage has no effect on contaminant removal -- it's purely for taste.
- ✓Tankless design -- fits where traditional RO systems won't
- ✓NSF 42, 53, 58, and 372 certified -- comprehensive coverage
- ✓600 GPD flow rate; smart LED faucet shows TDS and filter life
- ✓2:1 pure-to-drain ratio -- more efficient than traditional RO
- Proprietary filter cartridges -- locked into Waterdrop replacements
- Higher upfront and annual filter cost than APEC
- Thinner long-term track record than APEC
The right pick if under-sink space is the constraint. Comparable arsenic removal to the APEC in a significantly smaller footprint -- factor in the filter lock-in before committing.
- ✓5-stage RO removes arsenic, PFAS, lead, nitrates, fluoride, and chromium-6
- ✓No plumbing required -- ideal for renters in high-arsenic areas like Phoenix or Southwest
- ✓3:1 pure-to-drain ratio -- more efficient than traditional RO
- ✓No landlord conversation needed
- Filters into a reservoir -- not on-demand tap flow
- Takes up counter space
- Does not remineralize
For renters in high-arsenic areas who can't install under-sink, this provides full RO arsenic removal with zero installation. The only countertop format that addresses arsenic comprehensively.
The Bottom Line
Arsenic is the quiet contaminant -- tasteless, odorless, invisible, with health effects that accumulate over decades. The federal 10 ppb limit was never intended to mean "safe." If your municipal system reports arsenic, or if you have a private well in a high-risk area, reverse osmosis filtration for drinking and cooking water is the most straightforward and effective protection.
Related Articles
- How to Test Your Home's Drinking Water
- Phoenix, Arizona Water Quality 2026: Arsenic, Hard Water, and What Residents Should Filter
- Best Water Filter for Well Water
- Best Under-Sink Reverse Osmosis Systems
Sources: EPA Arsenic in Drinking Water · IARC Monographs on Arsenic · EWG Tap Water Database: Arsenic · USGS Arsenic in Ground Water of the United States · EPA Arsenic Treatment Technologies · NSF Certified Products Database