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 solvable problem. Millions of well owners deal with arsenic every year. The right treatment system can bring your water to safe levels. This page walks you through your options.

Not sure about your results yet? Start with a certified lab test. Learn how to test your well water here.

Want to understand more about arsenic and where it comes from? Read our full arsenic contaminant guide.

Why Arsenic Is a Problem in Well Water

Arsenic occurs naturally in rock and soil. It dissolves into groundwater over time. You cannot see it, smell it, or taste it. Long-term exposure is linked to serious health problems, including cancer, heart disease, and nerve damage.

The EPA (U.S. Environmental Protection Agency) sets the safe limit for arsenic in drinking water at 10 parts per billion (ppb). Private wells are not regulated by the EPA, so testing and treatment are up to you.

The Best Treatment Option: Reverse Osmosis

RO — reverse osmosis — is the most effective point-of-use treatment for arsenic. An RO system pushes water through a very fine membrane. That membrane blocks arsenic and other contaminants before the water reaches your tap.

Look for systems certified to NSF/ANSI 58. That certification means the system has been independently tested and proven to reduce arsenic.

RO systems are typically installed under the kitchen sink. They treat drinking and cooking water at one faucet. They are not whole-house systems.

Choosing the Right System for Your Situation

We organize our recommendations into three levels based on your test results and household needs.

Minimum

If your arsenic level is slightly elevated — below 10 ppb but above zero — and your household has no high-risk members, an entry-level RO system can do the job.

The Express Water RO5DX 5-Stage RO System ($150–$200, certified to NSF/ANSI 58) is the budget-conscious option that still works. It removes arsenic effectively and fits under most standard kitchen sinks.

Typical

Most well owners choose a mid-range system that balances performance, filter life, and cost.

The iSpring RCC7 7-Stage RO System ($200–$280, certified to NSF/ANSI 58) is what most well owners install. It adds extra filtration stages for broader contaminant coverage and consistently strong arsenic reduction.

  • 7-stage filtration removes arsenic plus sediment, chlorine, and other common well water issues
  • Strong track record with well water users
  • Replacement filters are widely available and affordable

High-Risk

Choose this level if your arsenic results exceed the EPA limit of 10 ppb, or if your household includes infants, pregnant women, or anyone with a weakened immune system.

The Aquasana OptimH2O RO + Claryum ($300–$400, certified to NSF/ANSI 58) is the option when results exceed the EPA limit or your household has infants or pregnant women. Its Claryum filtration technology is designed for maximum contaminant removal and provides an added layer of protection beyond standard RO.

  • Highest level of arsenic reduction available at this price point
  • Designed specifically for households with sensitive members
  • Combines RO with additional selective filtration stages

What About Whole-House Treatment?

RO systems treat water at one tap. If you want arsenic-free water at every faucet — including showers and laundry — you need a whole-house system. Whole-house arsenic treatment uses a different technology called adsorptive media filtration. These systems cost significantly more and require professional installation. Contact a licensed water treatment specialist if you need whole-house coverage.

Important Steps Before You Buy

  • Test first. Know your exact arsenic level before choosing a system. Find a certified lab near you.
  • Check your water chemistry. High iron or pH levels can affect how well RO systems perform on arsenic.
  • Replace filters on schedule. An RO system with expired filters will not protect you. Most systems need filter changes every 6–12 months.
  • Retest after installation. Confirm your new system is working. Test your treated water 4–6 weeks after setup.

Bottom Line

Arsenic in your well is a real risk — but treatment works. A certified RO system can reduce arsenic to safe levels for your family. Start with a reliable test, match your system to your results, and maintain it consistently.

Learn more about arsenic sources, health effects, and testing in our full contaminant guide.

Minimum

Express Water RO5DX 5-Stage RO System ($150–$200, NSF/ANSI 58)

Typical

iSpring RCC7 7-Stage RO System ($200–$280, NSF/ANSI 58)

High-risk

Aquasana OptimH2O RO + Claryum ($300–$400, NSF/ANSI 58)

Technical Overview: Arsenic Treatment for Private Wells

This section covers the treatment science, certification standards, water chemistry considerations, and performance validation protocols relevant to arsenic removal in residential well water systems. For background on arsenic occurrence, speciation, and health effects, see the full arsenic contaminant reference guide.

Treatment Mechanism: Reverse Osmosis

Reverse osmosis (RO) is the primary point-of-use technology recommended for residential arsenic reduction. RO membranes (typically thin-film composite, or TFC, polyamide) achieve arsenic rejection through a combination of size exclusion and charge repulsion. Effective pore diameter is approximately 0.0001 microns, well below the ionic radius of arsenate (As[V]) and arsenite (As[III]) species.

Arsenate (As[V]) — the predominant species in oxidizing, aerobic groundwater — carries a negative charge at typical groundwater pH (6.5–8.5). This enhances rejection by the negatively charged TFC membrane surface. Rejection rates for As(V) under certified test conditions commonly exceed 95%.

Arsenite (As[III]) — dominant in reducing, anaerobic conditions — is uncharged at near-neutral pH. RO membranes reject As(III) less efficiently, typically 70–85% under standard conditions. Pre-oxidation (chlorination, ozone, or potassium permanganate) converts As(III) to As(V) and is strongly recommended when source water speciation includes significant As(III) fractions. Well owners should request speciation analysis from a certified laboratory when total arsenic exceeds 5 ppb.

Certification Requirements

All RO systems recommended for arsenic reduction should carry certification to NSF/ANSI 58 (Reverse Osmosis Drinking Water Treatment Systems). NSF/ANSI 58 governs:

  • Material safety (extraction testing for all wetted components)
  • Structural integrity under pressure cycling
  • Contaminant reduction performance claims, including arsenic reduction under defined challenge water conditions

NSF/ANSI 58 arsenic challenge testing is conducted at:

  • Challenge concentration: 0.05 mg/L (50 ppb) arsenic (as pentavalent arsenate)
  • pH: 7.5 ± 0.5
  • Pressure: 60 psi (414 kPa) for standard residential systems
  • Required reduction: to ≤ 0.010 mg/L (10 ppb) — the EPA MCL (Maximum Contaminant Level)

Third-party certification bodies include NSF International, WQA (Water Quality Association), and IAPMO. Verify current certification status through the NSF product database before purchase, as certifications can lapse.

The following products carry NSF/ANSI 58 certification and are stratified by application level:

Minimum

The Express Water RO5DX 5-Stage RO System ($150–$200) meets NSF/ANSI 58 certification requirements and is appropriate for source water with low total dissolved solids (TDS) and arsenic concentrations modestly above background. A 5-stage configuration typically includes: sediment pre-filter, granular activated carbon (GAC) block, compressed carbon block, TFC RO membrane, and post-carbon polishing stage. Membrane rejection performance is adequate for As(V) in well-oxidized source water at this concentration range.

Typical

The iSpring RCC7 7-Stage RO System ($200–$280, NSF/ANSI 58) represents the standard installation for well owners with confirmed arsenic detections. The additional filtration stages — commonly including an alkaline remineralization or UV stage — extend pre-membrane protection and improve membrane longevity in source waters with moderate iron, hardness, or organic load. This configuration is suitable for arsenic concentrations up to the standard challenge level of 50 ppb, assuming adequate pre-treatment for As(III) conversion where required.

High-Risk

The Aquasana OptimH2O RO + Claryum ($300–$400, NSF/ANSI 58) integrates Claryum selective filtration media alongside the RO membrane. Claryum employs activated alumina and catalytic carbon components that provide adsorptive removal pathways for arsenic independent of membrane rejection, improving performance resilience when source water chemistry is variable. This system is indicated for arsenic concentrations exceeding the EPA MCL of 10 ppb, households with immunocompromised members, or source water with confirmed As(III) fractions where pre-oxidation is not feasible. The multi-mechanism approach provides a meaningful safety factor against membrane performance degradation between service intervals.

Water Chemistry Factors Affecting Performance

Several water chemistry parameters can significantly affect RO arsenic rejection efficiency and should be characterized before system selection:

  • pH: As(V) rejection increases with pH above 7.0 due to increased membrane surface charge density. Performance below pH 6.5 may be reduced; pH adjustment pre-treatment should be considered.
  • Total dissolved solids (TDS): Elevated TDS increases osmotic pressure, reducing net driving pressure across the membrane and lowering rejection efficiency at standard inlet pressures. Source water above 500 mg/L TDS may require booster pump installation.
  • Iron and manganese: Concentrations above 0.3 mg/L iron or 0.05 mg/L manganese can foul pre-filters rapidly and promote membrane scaling. Iron pre-filtration is required before the RO stage in affected wells.
  • Hardness: Calcium and magnesium at concentrations above 200 mg/L as CaCO₃ increase scaling risk on the RO membrane. Antiscalant dosing or water softening pre-treatment may be warranted.
  • Competing anions: Silica, phosphate, and fluoride can compete with arsenate for adsorption sites in systems using supplemental media (e.g., activated alumina). This is particularly relevant for high-risk-tier systems with adsorptive components.
  • Arsenic speciation: As noted above, the As(III)/As(V) ratio critically affects achievable rejection. Oxidation-reduction potential (ORP) measurement provides a field indicator of redox conditions; laboratory speciation analysis is recommended for arsenic above 5 ppb.

Performance Validation

System performance should be validated after installation and on a regular schedule thereafter:

  • Baseline testing: Collect both source (pre-treatment) and product water (post-RO) samples within 4–6 weeks of installation. Submit to a state-certified laboratory using EPA Method 200.8 or equivalent for total arsenic quantification. Detection limit should be ≤ 1 ppb.
  • Speciation follow-up: If baseline arsenic is above 5 ppb, request speciation to confirm As(III)/As(V) ratio and verify pre-oxidation strategy if implemented.
  • Ongoing monitoring: Annual retesting of product water is recommended at minimum. Quarterly testing is appropriate for high-risk households or systems treating source water above 20 ppb arsenic.
  • TDS rejection as a proxy: In-line TDS meters can serve as a continuous performance indicator. A product water TDS that rises to within 15% of source water TDS suggests membrane degradation and should trigger laboratory arsenic testing.

Maintenance Requirements

Maintenance failures are the most common cause of treatment system performance degradation in residential installations. Key requirements include:

  • Pre-filters: Sediment and carbon pre-filters should be replaced every 6–12 months depending on source water turbidity and organic load. Clogged pre-filters accelerate membrane fouling and reduce flow rate and rejection efficiency.
  • RO membrane: Typical service life is 2–5 years depending on source water quality, inlet pressure consistency, and pre-filter maintenance adherence. Membrane replacement should be triggered by declining product water flow rate, rising TDS rejection failure, or elapsed time per manufacturer specification — whichever occurs first.
  • Post-carbon polishing filter: Replace annually or per manufacturer recommendation. Exhausted post-carbon filters do not affect arsenic rejection but may allow tastes and odors from membrane permeate to pass through.
  • Adsorptive media (high-risk-tier systems): Activated alumina and catalytic carbon components have finite adsorptive capacity. Replacement intervals specified by the manufacturer are based on NSF/ANSI 58 challenge test volume throughput. Track actual household water consumption to accurately estimate exhaustion schedule rather than relying solely on calendar-based intervals.
  • Storage tank and sanitization: Annual sanitization of the pressurized storage tank with a dilute sodium hypochlorite solution is recommended to prevent biofilm formation. Flush thoroughly before return to service and retest product water after sanitization.

For comprehensive information on arsenic occurrence, regulated limits, health effects, and sampling protocols, refer to the arsenic contaminant guide.