Arsenic in Drinking Water: A Complete Homeowner's Guide

Arsenic is one of the more difficult drinking-water contaminants to detect because it provides virtually no sensory warning.

Water containing arsenic can still look clear, smell normal, and taste completely ordinary. The only reliable way to determine how much arsenic is present is through appropriate water testing.

Arsenic is not elevated in every water source. Risk varies considerably according to local geology, aquifer conditions, well depth, and other factors.

Whether you receive municipal water or use a private well, understanding where arsenic comes from, how it is measured, and which treatment technologies are designed to reduce it can help you make better decisions about your drinking water.

What Is Arsenic?

Arsenic is a naturally occurring element found in the Earth's crust.

It can occur in:

• Rock
• Soil
• Groundwater
• Surface water
• Air
• Some foods

In drinking-water discussions, the greatest concern is generally inorganic arsenic.

Unlike water-quality characteristics such as hardness or iron staining, arsenic cannot normally be detected by looking at or tasting the water.

Where Does Arsenic in Drinking Water Come From?

In many parts of the United States, arsenic in groundwater originates naturally.

As groundwater moves through underground rock and sediment, chemical conditions can cause naturally occurring arsenic to enter the water.

The process depends on:

• Local geology
• Mineral composition
• Groundwater chemistry
• pH
• Oxidation-reduction conditions
• Aquifer characteristics

This helps explain why arsenic concentrations can differ greatly among wells—even between properties relatively close to one another.

Can Human Activity Contribute?

Yes.

Arsenic has also been associated historically with activities such as:

• Mining
• Industrial processes
• Wood-preservation chemicals
• Some historical agricultural chemicals

However, naturally occurring geological sources are a major cause of elevated arsenic levels in groundwater across many regions of the U.S.

Where Is Arsenic Found in U.S. Groundwater?

Arsenic can occur in groundwater throughout the United States, but concentrations are not evenly distributed.

National groundwater studies have found that elevated arsenic is generally more common in parts of the western United States.

Areas with elevated groundwater arsenic also occur in portions of:

• The Midwest
• The Northeast
• Other localized geological settings

Likewise, living in a region associated with arsenic does not mean every well exceeds the drinking-water standard.

Public Water vs. Private Wells: An Important Difference

Where your water comes from determines who is responsible for monitoring it.

Public Water Systems

Community and non-transient, non-community public water systems must monitor for arsenic and meet the applicable standard.

Customers can review their utility's annual Consumer Confidence Report (CCR) for information about regulated contaminants detected in the system.

The CCR provides useful system-wide information, including:

• Water sources
• Detected regulated contaminants
• Applicable standards
• Monitoring results

Private Wells

Privately owned domestic wells are not regulated under the same federal drinking-water program.

The well owner is generally responsible for:

• Testing
• Maintenance
• Interpreting test results
• Selecting appropriate treatment when needed

If your home uses a private well, your local or state health department can often provide guidance on which contaminants to include in routine testing.

For more information, see our Well Water Testing and Treatment Guide.

How Can You Test Drinking Water for Arsenic?

Laboratory testing is the appropriate method for determining the arsenic concentration in drinking water.

Testing may be particularly useful when:

• You use a private well.
• The well has never been tested for arsenic.
• Nearby wells have reported elevated arsenic.
• State or local agencies identify arsenic as a regional concern.
• You are purchasing a home supplied by a private well.
• Your well has been significantly modified or replaced.

Use an Appropriate Laboratory

For reliable results, use a laboratory certified or approved for drinking-water analysis in accordance with your state requirements.

Your state drinking-water program or local health department can help identify laboratories that perform arsenic testing.

Ask What the Test Measures

A routine arsenic test generally reports total arsenic. It does not tell you how much is arsenite, As(III), versus arsenate, As(V). If that distinction affects treatment selection, ask the laboratory or treatment professional whether a separate speciation test is needed. Arrange its sampling and preservation procedure before collecting water.

Check the result, units, and reporting limit. “Not detected” means below a stated threshold, not necessarily zero. A reporting limit above 10 µg/L cannot establish whether a sample meets that benchmark. Basic bacteria/nitrate panels and TDS meters do not establish an arsenic concentration.

Follow local guidance on repeat testing. Minnesota’s well-water guidance illustrates how testing and treatment decisions depend on the result.

Understanding the EPA Standard for Arsenic

The federal Maximum Contaminant Level (MCL) for arsenic in regulated public drinking water is:

EPA adopted the 10 ppb standard in 2001, replacing 50 ppb, with compliance required by 2006 for covered systems. See EPA’s arsenic rule summary.

EPA's non-enforceable Maximum Contaminant Level Goal (MCLG) for arsenic is zero. The MCLG is a health goal, while the enforceable MCL takes treatment feasibility and other regulatory considerations into account.

That distinction is important: 10 ppb should not be interpreted as a boundary where arsenic is completely harmless below the number and harmful only above it. Long-term risk depends on concentration, duration of exposure, water consumption, and other factors.

Public-water compliance follows defined monitoring rules. For a private well, the federal MCL is a useful comparison benchmark, not an EPA compliance determination. State requirements or recommendations may be more protective.

Why Long-Term Arsenic Exposure Gets the Most Attention

Most concern about arsenic in drinking water involves chronic exposure to inorganic arsenic over extended periods.

The WHO arsenic fact sheet describes health concerns from long-term inorganic arsenic exposure, including skin lesions and cancers of the skin, bladder, and lungs. Other reported concerns include:

• Skin changes
• Cardiovascular effects
• Developmental and cognitive effects
• Diabetes-related effects
• Increased risk of certain cancers

The health significance for an individual depends on factors such as:

• Arsenic concentration
• Duration of exposure
• Amount of water consumed
• Other sources of arsenic exposure
• Age and health characteristics

Can You Remove Arsenic by Boiling Water?

No.

Boiling is useful for certain microbial water concerns, but it does not remove dissolved inorganic contaminants like arsenic.

Heating the water does not make the arsenic disappear.

If water evaporates while arsenic remains behind, the arsenic concentration in the remaining water can potentially increase.

What Should You Do if Your Arsenic Result Is Above 10 ppb?

If a private well test reports arsenic levels above 10 µg/L (10 ppb), do not try to solve the problem by boiling the water. Contact your state or local health department, arrange confirmation when advised, and use an alternative safe supply while treatment is selected and verified. Do not delay exposure-reduction steps while waiting for a repeat result.

Because arsenic exposure is primarily a concern from ingestion, treatment decisions usually focus first on water used for drinking and cooking. The appropriate response depends on the measured concentration, arsenic species, and overall water chemistry.

How Can Arsenic Be Reduced From Drinking Water?

If testing finds elevated arsenic, treatment should be selected based on the actual water chemistry rather than choosing a filter solely because its marketing mentions arsenic.

Technologies used for arsenic treatment can include:

Adsorptive Media

Specialized adsorptive media can bind arsenic as water passes through the treatment bed.

Examples include iron-based media and activated alumina formulations designed for arsenic treatment.

Reverse Osmosis

Reverse-osmosis systems use membrane separation and can reduce arsenic when properly selected and maintained.

Performance depends in part on the chemical form of arsenic and the water chemistry.

Ion Exchange

Specialized anion-exchange treatment can remove arsenate under suitable conditions. This is different from a conventional household cation-exchange water softener.

Competing ions in the water can affect performance, so treatment design should account for the results of a comprehensive water analysis.

Coagulation and Filtration

Larger water-treatment systems may use coagulation and filtration processes for arsenic removal.

These technologies require different operating conditions and maintenance. EPA’s arsenic treatment resources describe the technical factors behind their selection.

Why Arsenite and Arsenate Need Different Treatment Considerations

In groundwater, inorganic arsenic commonly occurs primarily in two forms:

• Arsenite — As(III)
• Arsenate — As(V)

Some treatment technologies remove arsenate more readily than arsenite.

For water with substantial arsenite, treatment may require a designed oxidation step to convert As(III) to As(V), followed by removal. Oxidation alone does not remove total arsenic. Do not assume standing water, boiling, or routine filter priming accomplishes the needed conversion.

This is another reason treatment should be based on actual water chemistry rather than generalized claims about a filter material.

Check the Exact Arsenic Certification

Look for a third-party listing with an explicit arsenic-reduction claim for the exact model and cartridge. Such claims may be limited to pentavalent arsenic, As(V), a specified incoming concentration, and defined operating conditions. A general NSF/ANSI 53 or 58 label does not establish every arsenic claim. Check the NSF contaminant-claims guide and product performance sheet.

Read any pretreatment requirements and rated capacity. A high percentage reduction is not enough: the treated-water concentration and continued performance matter.

Point-of-Use vs. Whole-House Arsenic Treatment

Another decision is whether treatment is needed only for drinking and cooking water or throughout the home.

Point-of-Use Treatment

A point-of-use system treats water at a particular location, typically the kitchen.

This may be appropriate when the treatment goal is specifically water used for:

• Drinking
• Cooking
• Coffee and tea
• Ice

Point-of-Entry Treatment

A point-of-entry or whole-house system treats water before it is distributed throughout the building.

These systems generally require more equipment, higher flow capacity, and professional treatment design.

Which approach makes sense depends on the test result, water chemistry, household use, and guidance from an appropriate water-treatment professional.

How to Evaluate Berkey® Arsenic Evidence

Black Berkey® and Phoenix Gravity elements have separate laboratory documentation. Review the Berkey® filter test-results library for the installed element’s report, rather than transferring claims between products.

For arsenic, check the tested chemical form, challenge concentration, pH, reporting limit, and service volume. A result labeled only “arsenic” does not establish equal performance for both As(III) and As(V). An initial test does not establish reduction through the advertised lifetime.

Laboratory testing is different from product certification. Chlorine/taste-and-odor certification does not establish arsenic reduction, and NSF/ANSI/CAN 372 concerns lead content in materials, not arsenic treatment.

If considering an arsenic-specific post-filter such as PF-2®, verify its current instructions, arsenic form, pretreatment conditions, and compatibility. A product name or the phrase “pre-oxidized arsenic” does not mean the filter itself performs the oxidation step.

For an arsenic-contaminated private well, select treatment with your health department or a qualified treatment professional and verify the finished water. Do not assume a gravity-fed system addresses other well-water contaminants or microbial safety. Use the replacement-filter guide for product compatibility.

What Should You Do If You're Concerned About Arsenic?

Frequently Asked Questions

Start With Your Water Result

Like many drinking-water contaminants, arsenic can be present at elevated concentrations without changing the water's appearance, smell, or taste.

For households receiving public water, the annual Consumer Confidence Report provides a useful starting point for understanding arsenic monitoring.

For private-well owners, testing is especially important because groundwater arsenic can vary considerably over relatively short distances and private wells are not routinely monitored by a public water supplier.

If a test identifies elevated arsenic levels, treatment should be selected based on the arsenic concentration, arsenic form, overall water chemistry, and the documented performance of the treatment system.

Last reviewed: October 17, 2026. Follow current local water notices and health-department guidance.