Arsenic in private-well water is a laboratory and public-health question before it is an equipment question. If a state-certified laboratory reports arsenic, keep the complete report, use another safe water source as directed, and contact the laboratory and local health or environmental department for result-specific guidance.
Do not try to clear the water through boiling, appearance, taste, a home test strip, or an in-home sales screening. When you compare treatment, require a certified arsenic-reduction claim for the exact model and check which arsenic form and feed-water conditions that claim covers.
First steps after an arsenic result
The CDC’s well-water guidance says not to drink well water that contains harmful chemicals, or is suspected of containing them. CDC advises using bottled water or water from another safe source and contacting the local health department for specific instructions.
Follow that guidance for all household uses the health department identifies. Ask a medical professional about personal exposure or health concerns. This article cannot interpret an individual health risk.
Boiling does not remove chemicals from water. It is not an arsenic treatment. Do not confuse instructions for microbial contamination with instructions for a chemical result.
Verify the laboratory report before selecting equipment
Contact the laboratory and read the report line by line. Confirm:
- The analyte is arsenic and how it is named on the report
- The units used and the laboratory’s reporting limit
- The sample date and exact collection point
- Whether the sample was collected before or after existing treatment
- Any qualifiers, flags, or notes attached to the result
- Whether another sample is recommended
- Which health or environmental department should interpret the result
Do not convert the value into different units unless the laboratory confirms the calculation. Do not compare it with a regulatory number copied from a product page or an article. Ask the health department which current standard or action level applies to the property and how the laboratory’s reporting format should be read.
The CDC well-testing page recommends state-certified laboratories and tells private-well owners to ask their health or environmental department which chemicals should be tested based on location. It identifies arsenic as one of the chemicals a well owner may need to test for.
A sample result describes a specific place and time
Write down where the sample came from. A result from untreated well water answers a different question from a result collected at a kitchen tap after treatment.
Record the condition of the well and treatment equipment at the time of sampling. Note recent well work, flooding, changes to plumbing, filter replacement, bypass use, or treatment adjustments. These facts help the laboratory or health department decide whether a confirmation sample or additional analysis is appropriate.
Do not assume a neighbor’s result describes your well. Do not use a public water provider’s report as evidence for a private source. Private-well decisions require a sample from the property.
Our guide to private-well testing in San Diego County explains how to preserve sample locations and treatment status so later reports can be compared.
Why the arsenic form matters when reading product claims
Product claims may be limited to a particular form of arsenic. EPA’s WaterSense product search for point-of-use reverse-osmosis systems identifies separate verified claims for pentavalent arsenic under stated conditions.
That does not establish performance for every arsenic result or every RO system. Ask the laboratory or treatment professional whether the available analysis gives enough information to evaluate a product claim. Then compare the report with the exact certification record and performance data sheet.
Do not assume one arsenic form, prescribe oxidation chemicals, or adjust pH based on a general guide. Those choices depend on laboratory evidence, complete water chemistry, equipment design, and professional oversight.
Treatment options depend on the complete water analysis
CDC says different home treatment systems remove different chemicals and instructs buyers to check the product label for the specific chemical of concern. It notes that reverse osmosis may reduce arsenic and that distillation removes arsenic, while common microfiltration does not remove dissolved chemicals such as arsenic.
That supports a shortlist for discussion, not a universal prescription.
Point-of-use reverse osmosis may be considered for drinking and cooking water when the exact model has a verified claim that matches the arsenic form and feed-water conditions. It creates treated and reject streams, requires filter and membrane maintenance, and leaves other fixtures untreated.
Adsorptive media or other arsenic-specific filtration may be considered when supported for the measured water chemistry and required flow. Media capacity, competing substances, pretreatment, change-out criteria, and spent-media handling are model-specific.
Ion exchange or another engineered process may be suitable in some designs. Do not treat a standard hardness softener as arsenic treatment without an exact certified claim.
Distillation is a point-of-use option recognized by CDC for arsenic removal, but it has energy, production-rate, cleaning, and volatile-chemical limitations. It is not automatic proof that all water in the home is treated.
Ultraviolet treatment and ordinary sediment or carbon filters should not be assumed to remove arsenic. UV addresses germs, and filter categories differ widely. Only an exact product claim provides the relevant evidence.
Decide which water needs treatment
A point-of-use system treats a selected faucet. A point-of-entry system treats water as it enters the home and must handle household flow and a larger treatment load. The right scope depends on current health-department guidance, how water is used, the laboratory result, and complete water chemistry.
Ask these questions before choosing the scope:
- Which uses require treated water under current health guidance?
- Which taps will and will not receive treated water?
- How will untreated and treated plumbing stay separated?
- What safe-water plan applies during maintenance or equipment failure?
- What daily volume and peak flow must the system handle?
- Where will backwash, reject water, brine, or spent media go?
Do not size a whole-house system from the arsenic result alone. Flow, other constituents, pretreatment, media capacity, and service intervals can change the design.
How to verify an exact treatment model
Ask the provider to give you:
- Full manufacturer and model number
- Certification organization and current listing
- Exact arsenic-reduction claim, including the arsenic form
- Influent limits and other test conditions in the performance data sheet
- Required pretreatment and incompatible water conditions
- Rated capacity or production and the replacement endpoint
- Monitoring method and sampling locations
- Filter, membrane, resin, or media replacement schedule
- Waste stream or spent-media handling instructions
- Written equipment, installation, testing, maintenance, and service charges
- Warranty terms and who is responsible for service
EPA’s product search can confirm WaterSense-labeled point-of-use RO models and their listed contaminant claims. It does not endorse a brand, guarantee availability, or cover every type of arsenic treatment.
A claim that a system “removes arsenic” without a model number, arsenic form, test conditions, and maintenance plan is incomplete. A percentage from a different product or laboratory setup does not establish performance in your well.
Plan confirmation and ongoing testing before installation
CDC says water treated for harmful chemicals should be tested to make sure treatment worked before it is used again. Set the confirmation plan with the state-certified laboratory and health department before installation.
The written plan should specify:
- Analyte and units
- Sample point before treatment, after treatment, or both
- Timing after startup
- Whether confirmation or repeat samples are needed
- Ongoing testing schedule
- Result that triggers media, membrane, or component service
- Safe-water procedure while the system is offline
Keep baseline, startup, and later reports together. Record service dates, replacement parts, bypass events, and any change to well or plumbing conditions. A treatment system needs continuing verification; installation alone is not proof of lasting performance.
Do not let a limited field test become a safety claim
A free in-home water test can help document basic water conditions and existing equipment. It cannot replace arsenic analysis by a state-certified laboratory or declare a private well safe.
Ask exactly what an in-home visit measures. If arsenic is the concern, bring the complete laboratory report and current public-health guidance. Do not accept an equipment recommendation that depends on an unmeasured value or an assumed arsenic form.
For broader context, read our well-water treatment guide and how home water-treatment systems differ.
Get help organizing the next step
Filter Pros San Diego is an independent information and referral site. We do not operate a laboratory, interpret medical risk, or promise that referred providers offer a particular arsenic system. We can arrange a free in-home water test and connect homeowners with separately licensed water-filtration professionals. The homeowner contracts with and pays the selected professional directly.
Call (858) 400-6508 or use our free in-home water test page to discuss a referral. Equipment availability, treatment capability, price, installation, and follow-up testing must be confirmed directly with the professional.
Frequently asked questions
Can you see, smell, or taste arsenic in well water?
Do not use appearance, smell, or taste to rule it out. Use a state-certified laboratory and follow local health-department guidance.
Does boiling remove arsenic?
No. CDC says boiling does not remove chemicals from water. Use another safe source and get result-specific public-health guidance.
Does every RO system reduce arsenic?
No. Verify the exact model, arsenic form, certified reduction claim, and performance-data conditions.
Will a carbon filter or UV system remove arsenic?
Do not assume so. UV is used for germs, not dissolved chemicals. Carbon products have different claims, and only an exact certified arsenic claim supports the decision.
How do I know an arsenic treatment is working?
Use follow-up samples from the locations and at the times specified by a state-certified laboratory and health department. Continue testing on their recommended schedule and follow the model’s service requirements.