Arsenic Water Filter Guide: Certified Claims, Private Wells and Arsenic III vs V
How to choose a water filter for arsenic, including NSF/ANSI 58 and 62 certified claims, activated alumina, anion exchange, arsenic III vs V oxidation, and private well testing.
Contaminants
Quick answer: For arsenic, test the water and find out whether the arsenic is arsenic III or arsenic V before choosing a filter. Reverse osmosis certified under NSF/ANSI 58 for pentavalent arsenic, activated alumina, anion exchange, and NSF/ANSI 62 distillation are recognized options. Standard carbon filters are not certified for arsenic reduction.
Best for
Private well owners in higher-risk regions and households with a water test showing arsenic.
Wrong fit
Emergency exposure situations. Contact a local health department or state lab first.
Tradeoff
Arsenic has no taste, smell, or color, and the right treatment depends on which form is in the water, not just the number on the test.
Arsenic does not announce itself.
Water with an arsenic result above the health limit can look, taste, and smell completely normal.
Quick Answer
Start with a certified lab test, not taste or appearance. If arsenic is present, the exact form matters: arsenic V (common in oxidized, chlorinated, or aerated water) is far easier to remove than arsenic III (common in anaerobic well water), which often needs oxidation before a filter can touch it. Reverse osmosis systems certified under NSF/ANSI 58 for pentavalent arsenic, activated alumina, anion exchange, and NSF/ANSI 62 distillation systems are the recognized treatment lanes. Plain activated carbon is not one of them.
Arsenic checklist
Step
Why it matters
Test with a certified lab
Arsenic cannot be detected by taste, smell, or color
Check your region
Coastal New England, the Southwest, and parts of the upper Midwest have more naturally occurring arsenic in groundwater
Ask about the form
Arsenic V is easier to treat; arsenic III may need oxidation first
Match the certified claim
NSF/ANSI 58 (reverse osmosis, pentavalent), NSF/ANSI 53 (activated alumina or anion exchange media), or NSF/ANSI 62 distillation
Skip plain carbon
Standard activated carbon is not certified for arsenic reduction
Maintain on schedule
Exhausted media stops reducing arsenic even though water still flows
Retest after installation
Confirms the system is actually working
Where arsenic comes from
Arsenic in drinking water is usually geological, not industrial. It occurs naturally in rock and sediment, and it dissolves into groundwater as minerals weather, which is why private wells carry more of the risk than treated public water.
The U.S. Geological Survey has mapped clear regional patterns. Coastal New England, particularly bedrock wells in Maine and New Hampshire, forms what USGS describes as an arsenic belt, with close to 30% of wells in those aquifers exceeding the federal health limit. The Southwest carries the highest national concentration, with USGS modeling showing predicted arsenic above the limit across 43% of basin-fill aquifer area in Arizona, Nevada, Utah, and neighboring states, and about 16% of sampled wells there exceeding the limit versus roughly 7% nationally. USGS has also flagged elevated arsenic in a glacial aquifer belt running from Ohio into Minnesota and the Dakotas, in southern Idaho, in West Texas, and in eastern Pennsylvania.
If you are on a private well in any of these regions, or you have simply never tested, arsenic belongs on the list. Public water systems are required to meet the federal arsenic limit; private wells are the owner's responsibility, and our private well water filter guide covers the full test-first workflow.
Why the EPA limit is set where it is
EPA and CDC's ATSDR classify inorganic arsenic as a known human carcinogen, and long-term exposure through drinking water is linked to cancers of the bladder, lung, skin, kidney, liver, and prostate. Non-cancer effects tied to years of exposure include skin changes, cardiovascular disease, and diabetes. These are chronic, long-term risks from sustained exposure over years, not a signal of acute danger from a single glass of water, and EPA set the current 10 ppb limit specifically to guard against that long-term exposure. This is exactly why testing matters more than symptoms: there is nothing to notice day to day.
Arsenic III vs arsenic V: why the form matters
Arsenic shows up in water in two chemical forms. Arsenic V (arsenate) is the more oxidized form and is more common in chlorinated municipal water. Arsenic III (arsenite) is the more reduced form and shows up more often in anaerobic well water. At typical drinking-water pH, arsenic V carries a negative charge, so it adsorbs onto treatment media and gets pulled out by ion exchange or reverse osmosis membranes. Arsenic III is largely uncharged at that same pH, so it passes through the same treatment much more easily.
Federal regulations for centralized treatment technologies spell this out directly: pre-oxidation may be required to convert arsenic III to arsenic V before the recognized treatment technologies work as intended. That is also why NSF/ANSI 58 certifies reverse osmosis systems specifically for "arsenic (pentavalent)" reduction, restricted to water already at or below a known concentration and valence of arsenic. In practice, this means a lab test that reports total arsenic without speciation may not tell you enough. If your result is elevated, ask the lab or a water treatment professional whether oxidation pretreatment is needed for your specific water.
Certified treatment options
Reverse osmosis, activated alumina, anion exchange, and distillation are the recognized paths, and the exact model still has to carry the certified claim.
Technology
What to check
Reverse osmosis
NSF/ANSI 58 certification listing "arsenic (pentavalent)," rated for your water's arsenic concentration
Activated alumina or anion exchange (pitcher, faucet, under-sink)
NSF/ANSI 53 certification for arsenic, using adsorptive media added specifically for the claim, not the base carbon
Distillation
NSF/ANSI 62 certified systems can carry a total arsenic reduction claim
Standard activated carbon
Not certified for arsenic reduction on its own; do not rely on a plain carbon pitcher or faucet filter
Our water filter certifications guide explains how to read an NSF, WQA, or IAPMO listing so you can confirm the exact claim before buying, and the reverse osmosis vs carbon comparison explains why the two technologies behave so differently on contaminants like this one. If your well test also raised nitrate, the nitrate water filter guide walks through a similar test-first, certification-first decision path.
A brand-level "removes arsenic" claim on the box is not the same as a certified model listing. Check the listing, not the packaging.
Testing your water
Public water systems test for arsenic under federal rules and report results in the annual water quality report; the guide to reading your water quality report shows where that number sits. Private wells are not covered by the same rules, and the well owner is responsible for testing. Use a certified laboratory, and if your result is elevated, or you are in a higher-risk region and have never tested, ask the lab whether it can report the arsenic III and arsenic V split so treatment can be matched correctly.
Because arsenic is geological rather than a fast-changing contaminant like bacteria, an unusually high first result, a change in well conditions, or new construction near the well are all reasons to retest, alongside whatever routine schedule your state health department recommends.
Frequently Asked Questions
Can a standard water filter pitcher remove arsenic?
Most standard carbon pitcher filters are not certified for arsenic reduction. Check the exact model listing before assuming a pitcher handles it.
Is reverse osmosis good for arsenic?
RO systems certified under NSF/ANSI 58 for pentavalent arsenic can be effective, but the certification is specific to arsenic V and to a rated concentration. Confirm the exact model and, if arsenic III is present, ask about oxidation pretreatment.
How do I know if my well has arsenic?
Test with a certified laboratory. Arsenic has no taste, smell, or color at any concentration, so appearance will not tell you.
Does boiling water remove arsenic?
Boiling does not remove arsenic and can concentrate it slightly as water evaporates. Boiling is a technique for pathogens, not for a dissolved mineral contaminant like arsenic.
Is a whole-house system necessary for arsenic?
Many households treat drinking and cooking water first with a certified point-of-use system. Whole-house treatment may be considered when a test result, local guidance, or other household uses support the larger investment.
These guides are built from manufacturer documentation, public specifications, primary research where health claims matter, and repeated buyer questions that show up in real ownership and installation decisions.
Manufacturer responses can clarify pricing bands, warranty terms, support footprint, or common mistakes. They do not move a page up the shortlist on their own.
