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.
Quick answer: Arsenic occurs naturally in rock and soil and can dissolve into groundwater. The federal Maximum Contaminant Level for arsenic in public drinking water is 10 parts per billion (10 µg/L). Public water systems monitor for arsenic, while private-well owners generally need to arrange their own 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.
In This Guide
- What Is Arsenic?
- Where Does Arsenic Come From?
- Where Is Arsenic Found in the U.S.?
- Public Water vs. Private Wells
- How to Test for Arsenic
- EPA Arsenic Standard
- Why Long-Term Exposure Matters
- Does Boiling Remove Arsenic?
- How Is Arsenic Reduced?
- Berkey® and Arsenic
- What Homeowners Should Do
- Frequently Asked Questions
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.
Clear water is not evidence that arsenic is absent. Taste, odor, and appearance are not reliable indicators of arsenic.
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 U.S. regions.
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
A state or county name alone cannot tell you whether your water has elevated arsenic. Groundwater conditions can vary locally, so testing your own well is more informative than relying on a broad regional map.
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
Public water systems subject to federal drinking-water regulations must monitor for arsenic and comply with the applicable federal 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.
Sampling matters. Follow the laboratory's instructions for bottle preservation, collection, and shipping. Improper sampling can reduce the usefulness of the result.
Understanding the EPA Standard for Arsenic
The federal Maximum Contaminant Level for arsenic in public drinking water is:
10 µg/L = 10 parts per billion (ppb) = 0.010 mg/L
This standard applies to regulated public water systems.
Utilities must monitor compliance with applicable requirements and take corrective action when they are not met.
The 10 ppb value is a regulatory standard. It should not be interpreted as a boundary where arsenic suddenly changes from completely harmless below 10 ppb to harmful above it.
Risk depends on concentration, exposure duration, and other individual and environmental factors.
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.
Long-term exposure to elevated inorganic arsenic has been associated with:
- Skin changes
- Cardiovascular effects
- Neurological 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
A water test cannot diagnose arsenic exposure in a person. If you are concerned about potential long-term exposure to arsenic or its health effects, discuss the situation with an appropriate healthcare professional.
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.
Boil-water advisories and chemical-contaminant treatment are different issues. A method appropriate for one type of water problem should not automatically be assumed to work for another.
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
Ion-exchange technology can be used to treat arsenic under appropriate conditions.
Competing ions in the water can affect performance, so treatment design should account for a comprehensive water analysis.
Coagulation and Filtration
Larger water-treatment systems may use coagulation and filtration processes for arsenic removal.
Iron-Based Treatment
Arsenic can interact strongly with iron oxides, which is why iron-based adsorptive treatment is commonly used for arsenic removal.
There is no universal “best arsenic filter” for every water source. Arsenic form, pH, competing ions, iron, manganese, and other aspects of water chemistry can affect treatment performance.
Why the Form of Arsenic Matters
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, an oxidation step may sometimes be used to convert As(III) to As(V) before the primary removal process.
This is another reason treatment should be based on actual water chemistry rather than generalized claims about a filter material.
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.
What About Berkey® Filters and Arsenic?
Black Berkey® Elements have manufacturer-published independent laboratory test results that include arsenic reduction.
The manufacturer reports arsenic reduction of up to 99.9% under the evaluated laboratory conditions.
That result should be interpreted in context.
Actual performance can vary according to:
- Starting arsenic concentration
- Arsenic form
- Water chemistry
- Competing contaminants
- Filter age
- Total gallons processed
- Correct installation and maintenance
Do not choose an arsenic treatment based only on the stainless-steel Berkey® vessel. Filtration performance comes from the specific filter element installed.
What About PF-2™ Fluoride and Arsenic Reduction Elements?
PF-2™ Fluoride and Arsenic Reduction Elements are optional secondary filters designed to be used beneath compatible primary Berkey® elements.
They are specifically intended to provide additional fluoride and arsenic reduction.
PF-2™ Elements are not standalone primary filters and should be installed and replaced in accordance with their product instructions.
See our PF-2™ Fluoride and Arsenic Reduction Filter page for current specifications and compatibility.
What About Phoenix Gravity Filters?
Phoenix Gravity New Millennium Edition™ Filters are a separate filter product with their own performance testing and specifications.
Do not assume that Black Berkey® test results automatically apply to Phoenix Gravity filters or vice versa.
For current Phoenix performance information, see our Water Filter Test Results page.
Choosing a Berkey® System Size
If you have already determined that a compatible gravity-fed filter configuration fits your water-treatment goals, choose the stainless-steel system size based primarily on household water use and countertop space.
| System | Capacity | Typical Fit |
|---|---|---|
| Travel Berkey® | 1.5 gallons | Individuals, couples, smaller kitchens |
| Big Berkey® | 2.25 gallons | Everyday household use |
| Royal Berkey® | 3.25 gallons | Households wanting greater capacity |
| Imperial Berkey® | 4.5 gallons | Higher daily water use |
| Crown Berkey® | 6 gallons | Large households and shared spaces |
See our Berkey® Water Filter Systems comparison guide for dimensions, capacities, and current filter configurations.
What Should You Do If You're Concerned About Arsenic?
1. Identify Your Water Source
Determine whether you receive regulated public water or use a private well.
2. Review Available Water-Quality Information
If you receive public water, check your Consumer Confidence Report for arsenic monitoring results.
3. Test a Private Well
If arsenic is a local concern—or your well has never been tested—use an appropriate certified drinking-water laboratory.
4. Interpret the Result Before Buying Treatment
Do not purchase a treatment system based solely on regional risk. Your own test result provides more useful information.
5. Consider the Complete Water Chemistry
If arsenic is elevated, other characteristics such as pH, iron, manganese, hardness, and competing ions can influence treatment selection.
6. Choose Treatment With Documented Arsenic Performance
Review arsenic-specific testing or certification for the exact treatment product rather than assuming any carbon, gravity, or membrane filter provides the same performance.
7. Maintain the Treatment System
Filters and treatment media have finite service lives. Follow the manufacturer's installation, maintenance, and replacement instructions.
8. Consider Follow-Up Testing
When arsenic treatment is being used for a known elevated concentration, follow-up testing can help confirm that the treatment system continues to perform as intended.
Frequently Asked Questions
Can I tell if my water contains arsenic by looking at it?
No. Arsenic generally does not produce a distinctive color, taste, or odor in drinking water. Laboratory testing is needed to determine its concentration.
What is the EPA limit for arsenic in drinking water?
The federal Maximum Contaminant Level for arsenic in regulated public drinking-water systems is 10 micrograms per liter, or 10 parts per billion.
Does every private well contain arsenic?
No. Arsenic occurrence depends strongly on local geology and groundwater chemistry. One well may have very low arsenic while another nearby well may have a higher concentration.
Are private wells regulated for arsenic by EPA?
Privately owned domestic wells are not covered by the same federal drinking-water regulations that apply to public water systems. Owners are generally responsible for testing and maintaining their well water.
How often should a private well be tested for arsenic?
There is no single schedule appropriate for every location. Follow your state or local health department's recommendations, especially in areas where arsenic is known to occur in groundwater.
Can boiling water remove arsenic?
No. Boiling does not remove arsenic. As water evaporates, arsenic remaining in the water can potentially become more concentrated.
Does a water softener remove arsenic?
A conventional household water softener should not automatically be assumed to provide reliable arsenic treatment. Treatment must be selected specifically for arsenic and the water's chemistry.
Does activated carbon remove arsenic?
Ordinary activated carbon should not be assumed to provide reliable arsenic reduction. Specialized adsorptive media or filters with arsenic-specific testing are more appropriate when arsenic is the treatment goal.
Can reverse osmosis reduce arsenic?
Reverse osmosis can reduce arsenic, but performance depends on system design, maintenance, water chemistry, and the chemical form of arsenic present.
What is the difference between arsenite and arsenate?
Arsenite, As(III), and arsenate, As(V), are two common inorganic forms of arsenic found in water. Some treatment processes remove arsenate more readily, which is why arsenic speciation and pretreatment can matter in certain applications.
Do Black Berkey® Elements reduce arsenic?
Manufacturer-published laboratory information reports arsenic reduction of up to 99.9% under the evaluated test conditions. Actual performance depends on water chemistry, arsenic concentration and form, filter condition, and proper use.
What are PF-2™ Filters used for?
PF-2™ Fluoride and Arsenic Reduction Elements are optional secondary filters designed to provide additional fluoride and arsenic reduction when used with compatible primary Berkey® filter elements.
Should I test again after installing an arsenic treatment system?
When a treatment system is used because testing identified elevated arsenic levels, follow-up testing can provide useful confirmation that treated-water concentrations remain within expected ranges.
Does my Consumer Confidence Report tell me about arsenic?
If arsenic is detected as part of required public water monitoring, the annual report provides relevant monitoring information and comparisons with applicable drinking water standards.
Final Thoughts
Arsenic is unusual among drinking-water contaminants because elevated concentrations can be present 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.
Don't try to detect arsenic with your senses or guess based on where you live. Test the water first, understand the result, and then choose treatment designed and evaluated for the conditions you actually have.