Best Water Filters for Arsenic (2026)
Choosing the right filter for arsenic III and arsenic V in well and municipal water
Data sources: EPA, CDC, NSF International, USGS Last updated: March 2026
ZipCheckup guide: Guide to water filters that remove arsenic from drinking water. Covers reverse osmosis, activated alumina, and iron-based adsorption — for well water and municipal systems.
Arsenic in Drinking Water
Arsenic is a naturally occurring element found in rock formations throughout the world. When groundwater flows through arsenic-bearing geological deposits, it dissolves arsenic into the water supply. This is the primary pathway for arsenic contamination in the United States.
Arsenic is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC). Long-term exposure through drinking water is associated with:
- Cancer — bladder, lung, skin, kidney, and liver cancer
- Cardiovascular disease — increased risk of heart disease and stroke
- Skin changes — thickening, discoloration, lesions (arsenicosis)
- Neurological effects — peripheral neuropathy, cognitive deficits in children
- Diabetes — association with increased Type 2 diabetes risk
- Reproductive effects — low birth weight, spontaneous abortion
The World Health Organization estimates that arsenic in drinking water is one of the top environmental health risks globally. In the U.S., approximately 2.1 million people drink from private wells with arsenic above the EPA MCL of 10 ppb.
Where Arsenic Is Found in the U.S.
Arsenic contamination is not evenly distributed. The highest concentrations occur in:
- Southwest — Arizona, Nevada, New Mexico, parts of California (natural volcanic deposits)
- Upper Midwest — Wisconsin, Minnesota, Michigan, parts of Illinois (glacial aquifer chemistry)
- New England — Maine, New Hampshire, Vermont (metamorphic rock bedrock)
- Pacific Northwest — parts of Oregon and Washington (volcanic geology)
- Great Plains — Nebraska, South Dakota, parts of Oklahoma (sandstone aquifers)
Agricultural areas with legacy pesticide use (lead arsenate, copper arsenate) may also have elevated arsenic levels in shallow groundwater.
Arsenic III vs. Arsenic V
Understanding the two forms of arsenic in water is essential for choosing the right filter:
| Property | Arsenic III (Arsenite) | Arsenic V (Arsenate) |
|---|---|---|
| Chemical form | As(III) — reduced | As(V) — oxidized |
| Found in | Groundwater (low oxygen) | Surface water, treated water |
| Charge at neutral pH | Neutral (uncharged) | Negatively charged |
| Ease of removal | Difficult | Easier |
| RO removal | 60–90% | 90–99% |
| Activated alumina | 10–50% | 85–99% |
| Iron-based media | 60–90% | 85–99% |
Pre-Oxidation: Converting Arsenic III to Arsenic V
If your well water contains arsenic III and you want to use activated alumina or iron-based media (which work better on arsenic V), a pre-oxidation step is necessary:
- Chlorination — adding a small amount of chlorine oxidizes arsenic III to arsenic V; requires contact time and may need dechlorination after
- Aeration — bubbling air through water adds dissolved oxygen, which slowly oxidizes arsenic (less effective than chlorination)
- Manganese dioxide — oxidizing filter media that converts arsenic III; available as a pre-filter stage
EPA Standards
| Standard | Level | Notes |
|---|---|---|
| MCL | 10 ppb (0.010 mg/L) | Enforceable standard for public water systems (effective 2006) |
| MCLG | 0 ppb | No safe level — arsenic is a known human carcinogen |
| WHO Guideline | 10 ppb | Same as EPA; some countries use 50 ppb (outdated) |
| New Jersey MCL | 5 ppb | Strictest state standard in the U.S. |
The EPA finalized the arsenic MCL of 10 ppb in 2001 (effective 2006), lowering it from the previous standard of 50 ppb. The MCLG is zero because arsenic is a known carcinogen with no identified threshold for cancer risk.
Filter Technologies That Remove Arsenic
Reverse Osmosis (RO)
RO is the most versatile arsenic removal technology because it effectively handles both arsenic III and arsenic V.
- Removes 90–99% of arsenic V and 60–90% of arsenic III
- No pre-oxidation required for arsenic III
- Also removes many other contaminants (lead, PFAS, nitrates, fluoride)
- NSF/ANSI 58 certified systems widely available
- Point-of-use under-sink units are affordable ($150–$500)
- Produces wastewater (2–4:1 ratio)
- Point-of-use only — does not treat whole-house water
- Removes beneficial minerals
- Lower arsenic III removal requires additional pre-oxidation for very high levels
Activated Alumina (AA)
Activated alumina is an aluminum oxide media with high surface area that adsorbs arsenic V through a chemical bonding process. It has been used in municipal arsenic treatment for decades.
- 85–99% removal of arsenic V
- Available as whole-house point-of-entry systems
- Long media life (6–12 months depending on concentration)
- Lower cost per gallon than RO for high-volume applications
- Does not produce wastewater
- Poor removal of arsenic III (10–50%) — requires pre-oxidation
- Performance depends heavily on water pH (optimal: 5.5–6.0)
- Alumina can leach small amounts of aluminum into water
- Requires pH adjustment for optimal performance in most well water
- Spent media is classified as hazardous waste in some states
Iron-Based Adsorption Media
Iron oxide and iron hydroxide media (including proprietary formulations like GFH, Bayoxide E33, and ArsenXnp) remove arsenic by adsorbing it onto the iron surface.
- 85–99% removal of arsenic V; moderate arsenic III removal (60–90%)
- Works across a wider pH range than activated alumina (pH 6.5–8.5)
- Available as whole-house and point-of-use systems
- No wastewater produced
- Better arsenic III performance than activated alumina (without pre-oxidation)
- Higher upfront cost ($500–$2,500 for whole-house)
- Media replacement cost ($100–$300/year)
- Iron media can impart slight taste/color if not properly sized
- Limited consumer retail availability — may require dealer installation
- Competing ions (phosphate, silicate) reduce arsenic capacity
Filter Comparison Table
| Feature | Under-Sink RO | Activated Alumina (POE) | Iron-Based Media (POE) | Iron-Based Media (POU) |
|---|---|---|---|---|
| Arsenic V Removal | 90–99% | 85–99% | 85–99% | 85–95% |
| Arsenic III Removal | 60–90% | 10–50% | 60–90% | 50–80% |
| Upfront Cost | $150–$500 | $300–$1,500 | $500–$2,500 | $80–$300 |
| Annual Maintenance | $50–$80 | $80–$200 | $100–$300 | $60–$120 |
| NSF Certification | NSF 58 | NSF 61 | NSF 61 | NSF 53/61 |
| Treats All Taps | No | Yes | Yes | No |
| Wastewater | Yes | No | No | No |
| pH Sensitivity | Low | High (needs pH 5.5–6) | Moderate | Moderate |
| Best For | Kitchen tap | Whole-house (municipal) | Whole-house (well) | Kitchen tap (well) |
For full RO system comparison, see the Best Under-Sink Reverse Osmosis Systems guide. Arsenic in wells is often coupled with iron, manganese, and H₂S — see Best Iron Filters for Well Water for sequenced treatment.
Well Water vs. Municipal Water
The source of your water fundamentally changes your arsenic treatment strategy:
Private Well Water
- Your responsibility. No federal agency monitors or treats private well water. You must test and treat.
- Likely arsenic form: Arsenic III (reduced) — the harder-to-remove form
- Water chemistry varies — pH, iron, manganese, hardness, and competing ions all affect filter performance
- Recommended approach: Under-sink RO for drinking water. Add whole-house iron-based media if arsenic exceeds 50 ppb or if bathing/inhalation exposure is a concern.
- Test annually at minimum. The EPA and most state health departments recommend annual testing for arsenic in private wells.
Municipal Water
- Your utility must comply with the 10 ppb MCL. If they exceed it, they must notify you and take corrective action.
- Likely arsenic form: Arsenic V (oxidized during treatment) — easier to remove
- Point-of-use filter is optional but recommended if your utility's levels are 5–10 ppb (legal but still above the MCLG of 0)
- Check your water report: Your annual Consumer Confidence Report (CCR) lists arsenic testing results. If it shows "ND" (not detected) or <5 ppb, arsenic is unlikely to be a concern.
Recommendations
Best Option for Well Water: Under-Sink RO
If you're on a private well with confirmed arsenic:
- Install an NSF/ANSI 58 certified under-sink RO system at the kitchen tap
- Use the RO tap for all drinking and cooking water
- If arsenic III is dominant and levels are very high (>50 ppb), consider a pre-oxidation step (chlorine injection or manganese dioxide filter) before the RO system
Price range: $150–$500 installed. Annual filters: $50–$80.
View top-rated RO systems for arsenic →
Best Whole-House Option: Iron-Based Adsorption
For households that need arsenic treatment at every tap:
- Install a point-of-entry iron-based adsorption system sized for your water flow rate
- Test inlet and outlet water quarterly for the first year to confirm performance
- Pair with an under-sink RO at the kitchen tap for maximum drinking water protection
Price range: $500–$2,500 installed. Annual media replacement: $100–$300.
View whole-house arsenic treatment systems →
Best Budget Option: Point-of-Use Iron Media Cartridge
For moderate arsenic levels (10–30 ppb) in well water:
- Install an iron-based adsorption cartridge under the kitchen sink
- Choose a system specifically rated for arsenic (not just general iron removal)
- Replace cartridges on schedule — arsenic breakthrough happens without warning
Price range: $80–$300. Annual cartridge replacement: $60–$120.
View point-of-use arsenic filters →
How to Test for Arsenic
Step 1: Check Existing Data
- Municipal water: Request your utility's Consumer Confidence Report (CCR) or check ZipCheckup for reported data
- Well water: Check USGS groundwater data for your county — the USGS Water Resources database includes arsenic measurements from sampled wells in your area
Step 2: Lab Testing
For private wells or to verify your filter's performance:
- Use a state-certified drinking water lab (find one through your state drinking water program)
- Request speciated arsenic testing (arsenic III and arsenic V separately) — this is critical for choosing the right filter technology
- Cost: $25–$50 per sample at most state labs; speciated testing may cost $50–$100
Step 3: Interpret Results
| Result | Risk Level | Action |
|---|---|---|
| <3 ppb | Low | No filter needed for arsenic |
| 3–10 ppb | Moderate | Consider a filter, especially for long-term residents and children |
| 10–50 ppb | High | Install a certified filter. If on a public system, this is an MCL violation. |
| 50–100 ppb | Very High | Install a filter immediately. Consider whole-house treatment. Get speciated testing. |
| >100 ppb | Extreme | Do not use for drinking or cooking until treated. Contact your state health department. Consider bottled water as interim solution. |
Maintenance and Annual Costs
Arsenic filters must be maintained on schedule. Unlike chlorine or taste/odor filters, there is no perceptible change when an arsenic filter is exhausted — the water looks, tastes, and smells the same.
Replacement schedule:
| Component | Replace Every | Cost |
|---|---|---|
| RO pre-filters | 6–12 months | $15–$30 |
| RO membrane | 2–3 years | $30–$60 |
| RO post-filter | 12 months | $10–$20 |
| Activated alumina media (POE) | 6–12 months | $50–$150 |
| Iron-based media (POE) | 12–24 months | $100–$300 |
| Iron-based cartridge (POU) | 3–6 months | $30–$60 each |
Total annual cost by system type:
| System | First-Year Cost | Annual Cost (Year 2+) |
|---|---|---|
| Under-sink RO | $200–$580 | $50–$80 |
| Activated alumina (POE) | $380–$1,700 | $80–$200 |
| Iron-based media (POE) | $600–$2,800 | $100–$300 |
| Iron-based cartridge (POU) | $140–$420 | $60–$120 |
Frequently Asked Questions
Do Brita or PUR filters remove arsenic?
Standard Brita and PUR pitcher filters are NOT effective at removing arsenic. These use granular activated carbon which does not adsorb arsenic. You need a reverse osmosis system, activated alumina filter, or iron-based adsorption media specifically designed for arsenic removal.
Does boiling water remove arsenic?
No. Like PFAS and lead, boiling water concentrates arsenic rather than removing it. Arsenic is a dissolved inorganic element that does not evaporate with steam. Use a certified filter for arsenic removal.
Is arsenic more common in well water or city water?
Arsenic is significantly more common in private well water because wells tap directly into groundwater that may flow through arsenic-bearing rock formations. Municipal systems are required to treat water to meet the 10 ppb MCL. Private wells have no federal treatment requirement — testing and treatment are the homeowner's responsibility.
What is the difference between arsenic III and arsenic V?
Arsenic III (arsenite) is the reduced form found in oxygen-poor groundwater. Arsenic V (arsenate) is the oxidized form found in surface water and treated municipal supplies. Arsenic III is harder to remove with most filters. Reverse osmosis handles both forms, but activated alumina and iron-based media work primarily on arsenic V. Pre-oxidation (chlorination or aeration) converts arsenic III to arsenic V for easier removal.
How much does it cost to filter arsenic from well water?
An under-sink RO system costs $150–$500 and is the most cost-effective option for drinking water. A whole-house iron-based adsorption system for well water costs $500–$2,500 plus $100–$300/year in media replacement. Activated alumina point-of-entry systems cost $300–$1,500. Total annual cost for most households is $100–$300 after the initial investment.
How often should I test my well for arsenic?
The EPA recommends testing private wells annually for arsenic. If your initial test shows arsenic above 5 ppb, test every 6 months to track trends. After installing a treatment system, test the treated water quarterly for the first year and then annually to confirm the filter is working.