Arsenic has no color, no odor, and no taste at concentrations that matter. At 20 ppb, twice the EPA limit, your water looks and tastes completely normal. The only way to know is a test.
If your test shows arsenic above 10 ppb, you need treatment. Here’s how to pick the right one.
Step 1: Test Before You Do Anything Else
Don’t guess at arsenic levels based on geography or your neighbor’s experience. Wells 100 feet apart can have very different readings.
A certified lab test for arsenic costs $15 to $50. It tells you three things you need to make a good treatment decision:
- Your arsenic concentration in ppb (micrograms per liter)
- Whether you’re above or below the EPA maximum contaminant level of 10 ppb
- Your water’s pH, which affects which treatment technology performs best
The EPA’s maximum contaminant level (MCL) for arsenic is 10 ppb. The maximum contaminant level goal (MCLG) is 0, meaning EPA considers no level safe from a health standpoint. Treatment decisions should reflect that context.
See Best Mail-In Water Tests for certified lab options that include arsenic panels.
Step 2: Know Which Form of Arsenic You Have
Arsenic in groundwater comes in two main forms, and they don’t behave the same way during treatment.
Arsenic (V), also called arsenate, is the oxidized form. It’s the most common type in oxygenated groundwater. Most treatment technologies target it well.
Arsenic (III), also called arsenite, is the reduced form. It shows up in low-oxygen groundwater, particularly in some deep wells. It’s harder to remove. Some filters are rated for arsenic (V) only.
A standard lab test reports total arsenic. A more detailed well assessment or speciation test can indicate the breakdown between forms. In practice, arsenic (V) is far more common in U.S. drinking water sources. But if your water comes from a deep, low-oxygen well and treatment isn’t producing the results you expect, arsenic (III) may be a factor worth investigating with your state health department or a water treatment professional.
If you’re on a private well, the Well Water Testing Guide covers when to request a full water quality panel.
Step 3: Choose a Treatment System
Point-of-Use Treatment (Recommended Starting Point)
Point-of-use systems treat water at one tap, typically your kitchen sink. That covers drinking and cooking, which are the main ingestion exposure pathways. Dermal absorption of arsenic from bathing at typical well water concentrations is considered minimal compared to ingestion, so whole-house treatment usually isn’t needed.
Reverse osmosis (NSF/ANSI 58)
This is the most practical option for most households. An under-sink RO system installs below your kitchen sink and delivers filtered water through a dedicated faucet.
NSF/ANSI 58 is the certification standard for RO drinking water systems. A system certified under NSF 58 for arsenic reduction has demonstrated 95%+ reduction in certified testing. Most RO membranes handle both arsenic (V) and arsenic (III), but verify the specific model’s certification covers arsenic before buying.
Cost: $150 to $400 for the unit, plus $50 to $100 per year in filter replacements. Membrane replacement typically runs every 2 to 5 years.
See the full comparison: Best Under-Sink RO Systems
Activated alumina
Activated alumina is specifically effective for arsenic. It’s used in both point-of-use and whole-house systems. It works well for both arsenic (V) and arsenic (III). Performance is best at pH below 6.5, which is worth checking against your test results. If your water pH is higher, pre-acidification or a different treatment method may work better.
Ion exchange (strong base anion resin)
Effective for arsenic (V). Less effective for arsenic (III) without a pre-oxidation step to convert it first. More commonly used in point-of-entry systems than under-sink.
Whole-House Treatment (When You Need It)
Most families don’t need it. But if arsenic levels are very high, or if you want whole-home coverage, whole-house arsenic treatment is possible.
Typical setup: an oxidation step (usually air injection or a chemical oxidant) to convert arsenic (III) to arsenic (V), followed by media filtration using activated alumina or a similar material. These systems are more complex and more expensive, usually $2,000 to $6,000 installed. They require ongoing media maintenance and monitoring.
For most households with well water arsenic at or moderately above 10 ppb, point-of-use at the kitchen tap is the right first step.
Learn more about arsenic in your water: Arsenic Contaminant Profile
What Won’t Remove Arsenic
Standard activated carbon filters (Brita pitchers, most under-sink carbon units, countertop filters) do not remove arsenic. NSF 42 and NSF 53 certifications don’t require arsenic testing. A filter that’s great for chlorine taste won’t touch arsenic.
Boiling concentrates arsenic. As water evaporates, dissolved arsenic stays behind. Never use boiling as arsenic treatment.
Water softeners are built for hardness minerals like calcium and magnesium. They’re not effective for arsenic removal.
Distillation is technically effective but impractical for daily household volumes. The production rate is too slow for a full family’s drinking and cooking needs.
Step 4: Maintain Your System and Retest
Treatment systems have finite lifespans. An RO membrane approaching the end of its life will show declining rejection rates. Activated alumina media eventually saturates.
After installing treatment, retest your water at 6 months. Use the same certified lab so results are directly comparable. If the treated water shows arsenic above your target level, the media or membrane needs replacement.
For RO systems, a TDS meter is a cheap way to monitor membrane performance between lab tests. As TDS in the filtered water climbs, rejection is declining.
Set a calendar reminder. Testing costs far less than exposure from a failing system you assumed was still working.
Geographic Context
Arsenic occurs naturally in bedrock and soil across the U.S. Private wells in Maine, New Hampshire, Arizona, Nevada, and parts of the rural Midwest and Southwest tend to show higher arsenic concentrations. State health departments in these areas often publish local data and sometimes offer low-cost or free testing programs.
If you’re in a higher-risk area and haven’t tested your well recently, start there. A single lab test is cheap. Knowing your number is the only way to make a good decision.
The Direct Recommendation
Test your water before choosing a treatment system. Arsenic levels and water chemistry vary by region and well.
For most households, an NSF/ANSI 58-certified under-sink RO system is the best combination of effectiveness, convenience, and cost for arsenic reduction. Install it at the kitchen tap. Retest at 6 months to confirm performance. Replace filters on schedule.
That covers the primary exposure pathway at a fraction of the cost of whole-house treatment. Start there.