Treatment Guide

Arsenic Treatment for Well Water

Certified treatment options for private wells with arsenic in the water. Compare systems by protection level and budget.

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Arsenic in Your Well Water: What to Do Next

Finding arsenic in your well water is serious — but it's a problem you can fix. Arsenic is a naturally occurring element that seeps into groundwater from rock and soil. It has no taste or smell, so testing is the only way to know it's there.

Before you choose a treatment system, make sure you have a recent test result in hand. Learn more about arsenic in well water on our arsenic contaminant guide. If you haven't tested yet, start at our water testing page.

How Treatment Works

The most proven method for removing arsenic from drinking water is reverse osmosis (RO). RO systems push water through a very fine membrane. That membrane blocks arsenic and other contaminants. The clean water goes to your tap. The rest goes down the drain.

Point-of-use RO systems treat water at one faucet — usually the kitchen sink. This is where most people get their drinking and cooking water. These systems are effective, affordable, and easy to maintain.

Which System Is Right for You?

Your test results and household situation will guide your choice. Here are three tiers to consider:

Minimum

If your arsenic level is low and your budget is tight, the APEC ROES-50 Essence 5-Stage Reverse Osmosis System ($277, certified to NSF/ANSI 58 — the national standard for RO drinking water systems) gets the job done. It's a reliable entry-level option that still meets the key safety certification you should require from any RO system.

Typical

The American Made Reverse Osmosis System ($628, NSF/ANSI 58 certified) is what most well owners install. It offers stronger build quality and longer filter life, making it a smart middle-ground investment for everyday household use.

High-Risk

If your arsenic results exceed the EPA's maximum contaminant level of 10 micrograms per liter (10 µg/L), or if your household includes infants or pregnant women, choose the Pioneer Whole-House Lead, Cyst & PFOA/PFOS Removal System ($1,669, certified to NSF/ANSI 53 and 58). This system treats water at every tap in your home, not just the kitchen.

What About the Rest of the House?

Point-of-use systems protect your drinking and cooking water. They do not treat shower water or laundry water. For most people, this is fine — arsenic exposure through skin contact is much lower risk than swallowing it.

If you want protection at every faucet, a whole-house system like the Pioneer is the right call.

Maintenance Matters

No system works forever without upkeep. Keep these points in mind:

  • Replace RO membranes every 2 to 3 years
  • Replace pre-filters every 6 to 12 months
  • Retest your water every year to confirm the system is working
  • Keep records of your filter change dates

Next Steps

  • Have a test result? Match your arsenic level to the right tier above.
  • Not tested yet? Visit our water testing page to find a certified lab.
  • Want to understand your results? Read our full arsenic contaminant guide.

Minimum

APEC ROES-50 Essence 5-Stage Reverse Osmosis System ($277, NSF/ANSI 58)

Typical

American Made Reverse Osmosis System ($628, NSF/ANSI 58)

High-risk

Pioneer Whole-House Lead, Cyst & PFOA/PFOS Removal System ($1,669, NSF/ANSI 53/58)

Arsenic Treatment in Private Wells: Technical Reference

This section covers treatment mechanisms, certification requirements, water chemistry considerations, performance validation, and maintenance protocols for arsenic removal in private well water systems. For a full overview of arsenic occurrence, health effects, and regulatory context, see the arsenic contaminant guide.

Primary Treatment Mechanisms

Arsenic in groundwater occurs predominantly in two oxidation states: arsenite (As(III)) and arsenate (As(V)). Arsenate is more readily removed by most treatment technologies. Arsenite typically requires pre-oxidation — using chlorine, potassium permanganate, or aeration — to convert it to arsenate before effective removal can occur.

Proven removal technologies include:

  • Reverse Osmosis (RO): Pressure-driven membrane separation. Effective against both arsenate and, to a lesser degree, arsenite. Rejection rates for arsenate typically exceed 95% under standard operating conditions.
  • Activated Alumina (AA): Adsorption-based media. Highly effective for arsenate removal. pH-sensitive; optimal performance occurs between pH 5.5 and 6.0.
  • Iron-Based Media: Adsorbs arsenate via ligand exchange. Effective over a broader pH range than activated alumina. Competing anions (phosphate, silica, vanadium) can reduce capacity.
  • Coagulation/Filtration: Used in larger systems; less common at the point-of-use (POU) or point-of-entry (POE) scale for private wells.

NSF/ANSI Certification Requirements

Certification is the primary assurance of a system's performance claim. Two standards govern arsenic treatment products at the residential scale:

  • NSF/ANSI 58: Governs RO systems. Requires testing and certification of contaminant reduction claims, including arsenic (As(V) and, in some certifications, As(III)), structural integrity, and material safety. All three recommended systems carry NSF/ANSI 58 certification.
  • NSF/ANSI 53: Governs activated carbon and other media-based systems making health-effects reduction claims. The Pioneer Whole-House Lead, Cyst & PFOA/PFOS Removal System ($1,669) carries both NSF/ANSI 53 and NSF/ANSI 58 certifications, providing broader contaminant coverage appropriate for high-risk installations.

Installers and specifiers should verify that the specific arsenic reduction claim — not just general certification — appears on the manufacturer's NSF product listing at info.nsf.org.

Water Chemistry Factors Affecting Performance

Arsenic removal efficiency is sensitive to several source water parameters. A full water chemistry panel should be completed before system selection. Key variables include:

  • pH: Elevated pH (above 7.5) reduces RO membrane rejection rates for arsenite. Activated alumina performance degrades above pH 8.0.
  • Total Dissolved Solids (TDS): High TDS increases osmotic pressure against the RO membrane, reducing flux and requiring higher operating pressure to maintain throughput.
  • Competing Anions: Phosphate, silica, fluoride, and vanadium compete with arsenate for adsorption sites on media-based systems. Elevated concentrations of these anions reduce effective capacity and service life.
  • Iron and Manganese: Concentrations above 0.1 mg/L can foul RO membranes or media beds. Pre-treatment filtration is required when these constituents are elevated.
  • Arsenic Speciation: If source water contains significant As(III), pre-oxidation must be incorporated upstream of the primary treatment unit. Without speciation data, assume As(III) is present and design accordingly.
  • Hardness: Hard water accelerates membrane scaling. Anti-scalant dosing or softening pretreatment may be required for RO systems above 7 grains per gallon (120 mg/L as CaCO₃).

Performance Tiers and Application Guidance

Minimum

The APEC ROES-50 Essence 5-Stage Reverse Osmosis System ($277, NSF/ANSI 58) is appropriate where influent arsenic is detectably above background but remains below the EPA Maximum Contaminant Level (MCL) of 10 µg/L, source water chemistry is not complex, and the installation is a standard point-of-use kitchen application. This system meets minimum certification requirements for arsenic reduction claims under NSF/ANSI 58.

Typical

The American Made Reverse Osmosis System ($628, NSF/ANSI 58) represents the standard specification for residential well treatment. It is appropriate for arsenic concentrations near or moderately above the 10 µg/L MCL, with standard water chemistry. Higher-grade components and longer membrane life reduce lifecycle cost compared to entry-level systems.

High-Risk

The Pioneer Whole-House Lead, Cyst & PFOA/PFOS Removal System ($1,669, NSF/ANSI 53/58) is the appropriate specification when arsenic concentrations significantly exceed the 10 µg/L MCL, when vulnerable occupants (infants, pregnant women, immunocompromised individuals) are present, or when co-occurring contaminants — including lead, cysts, PFOA, or PFOS — are detected or suspected. Whole-house POE installation ensures treated water at all points of consumption and dermal contact.

Performance Validation

Installation of a certified system does not guarantee in-situ performance. Validation testing is required to confirm efficacy under actual operating conditions:

  • Collect paired influent and effluent samples within 30 days of system startup.
  • Submit samples to a state-certified laboratory using EPA Method 200.8 or equivalent for arsenic speciation if needed.
  • Target effluent concentration: below 10 µg/L (EPA MCL); below 5 µg/L is achievable and preferable for vulnerable households.
  • Retest annually, and immediately following any change in source water conditions, pressure loss, or filter replacement.

Maintenance Protocols

Performance degradation in RO systems typically manifests as increasing TDS passage through the membrane. Establishing a maintenance schedule tied to water volume processed — rather than calendar time alone — improves reliability:

  • Sediment and carbon pre-filters: Replace every 6 months, or sooner if pressure drop across the system exceeds 15 psi from baseline.
  • RO membrane: Replace every 24 to 36 months under typical residential use conditions. High TDS or iron in source water shortens membrane life.
  • Post-carbon polishing filter: Replace annually.
  • Media-based systems (activated alumina, iron media): Monitor effluent arsenic concentration quarterly. Bed exhaustion is not visible — only effluent testing confirms remaining capacity. Regeneration (for AA) or media replacement schedules should be set by the manufacturer's throughput specifications, adjusted for actual influent concentration and competing anion load.
  • Whole-house POE systems: Follow manufacturer-specified backwash cycles. Inspect housings and connections semi-annually for microbial contamination points.

For regulatory context, health effects data, and MCL reference information, see the arsenic contaminant guide.