Arsenic in Drinking Water: A Complete Guide
Understanding arsenic contamination, its serious health risks, and how to protect your family from this naturally occurring toxic element.
Environmental Health Research
Expert Reviewed
This content has been reviewed by Dr. Sarah Chen, PhD, Environmental Science Advisor, to ensure accuracy and alignment with current environmental science standards.
Last reviewed: April 2026
What Is Arsenic and How Does It Get in Water?
Arsenic is a naturally occurring element found in rocks, soil, and groundwater throughout the world. Unlike many water contaminants caused primarily by human activity, arsenic contamination in drinking water most often comes from natural geological sources.
Natural Sources (Most Common)
Arsenic naturally occurs in certain rock formations and dissolves into groundwater over time:
- Volcanic deposits: Regions with volcanic activity often have higher arsenic levels
- Sedimentary rock: Certain formations release arsenic as water flows through
- Geothermal activity: Hot springs and geothermal areas concentrate arsenic
- Aquifer conditions: pH, oxygen levels, and other factors affect arsenic release
Human-Caused Contamination
Industrial and agricultural activities can also introduce arsenic:
- Mining operations: Copper, gold, and lead mining releases arsenic
- Historical pesticides: Lead arsenate was used in orchards until the 1940s
- Wood preservatives: CCA-treated wood (pre-2004) contains arsenic
- Industrial waste: Semiconductor manufacturing and other industries
- Coal combustion: Ash and waste from power plants
Two Forms of Arsenic
Arsenic exists in two primary forms in water:
- Arsenite (As III): More toxic and more difficult to remove; common in groundwater with low oxygen
- Arsenate (As V): Less toxic and easier to remove; common in oxygen-rich surface water
Many treatment systems first oxidize arsenite to arsenate for more effective removal.
Health Effects of Arsenic Exposure
Arsenic is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC). Long-term exposure to arsenic in drinking water causes serious health problems.
Arsenic Is a Known Human Carcinogen
The EPA, WHO, and IARC all classify arsenic as carcinogenic to humans based on extensive evidence from populations exposed to arsenic-contaminated water.
Cancer Risks
Long-term arsenic exposure increases risk of:
- Skin cancer: Most well-documented link; multiple types
- Bladder cancer: Strong evidence of increased risk
- Lung cancer: Even without smoking exposure
- Kidney cancer: Elevated risk with chronic exposure
- Liver cancer: Associated with high-level exposure
Non-Cancer Health Effects
Cardiovascular Disease
- Increased risk of heart disease and stroke
- High blood pressure
- Peripheral vascular disease ("blackfoot disease")
Skin Changes
- Skin lesions and discoloration
- Thickening of palms and soles (hyperkeratosis)
- Small warts or corns (precancerous)
Neurological Effects
- Peripheral neuropathy (numbness, tingling)
- Cognitive impairment in children
- Developmental delays
Other Effects
- Diabetes (some studies show increased risk)
- Immune system suppression
- Reproductive problems
- Gastrointestinal effects at high doses
Children and Pregnancy
Vulnerable Populations:
- Children: May experience cognitive and developmental effects; more susceptible due to higher water intake relative to body weight
- Pregnant women: Arsenic crosses the placenta; associated with low birth weight and infant mortality
- Infants: Formula mixed with arsenic-contaminated water poses significant risk
EPA Regulations and Safe Levels
The EPA significantly strengthened arsenic standards in 2001, reducing the allowed level from 50 ppb to 10 ppb. This change was based on improved understanding of arsenic's cancer-causing effects.
Current EPA Standards
- Maximum Contaminant Level (MCL): 10 ppb (0.010 mg/L)
- Maximum Contaminant Level Goal (MCLG): 0 ppb (zero)
The Goal Is Zero:
The EPA's health goal (MCLG) for arsenic is zero because there is no known safe level. The enforceable standard of 10 ppb balances health protection with treatment feasibility and cost.
Understanding Arsenic Levels
- Below 3 ppb: Low level, minimal concern
- 3-10 ppb: Below MCL but not zero; some health advocates recommend action
- Above 10 ppb: Exceeds EPA limit; requires treatment or alternative source
- Above 50 ppb: High level; immediate action needed
Private Wells Are Not Regulated
Important: EPA regulations only apply to public water systems. If you have a private well, you are responsible for testing and treatment. This is especially critical in regions known for naturally occurring arsenic.
State Variations
Some states have adopted stricter standards than the federal EPA limit:
- New Jersey: 5 ppb MCL
- New Hampshire: 5 ppb action level for schools
Check your state's regulations, which may provide additional protection.
Testing for Arsenic
Arsenic is colorless, odorless, and tasteless. Testing is the only way to know if your water contains arsenic.
Who Should Test
Testing is essential if:
- You have a private well
- You live in a region known for arsenic (see below)
- You are pregnant or have young children
- Your area has mining or industrial history
- You have never tested your well water
Testing Options
1. Certified Laboratory Testing (Recommended)
- Cost: $15-50 for arsenic alone; $100-200 for comprehensive panel
- Accuracy: Highest accuracy, can detect very low levels
- Where to find: State-certified labs, EPA website
- Turnaround: 5-10 business days typically
2. Home Test Kits
- Cost: $15-40
- Accuracy: Lower than lab testing; may have higher detection limits
- Best for: Initial screening
- Note: If home test shows arsenic, confirm with lab test
3. Public Water System Data
- Check your annual Consumer Confidence Report (CCR)
- Contact your water utility for recent test results
- Use our water quality search to find your city's data
Sample Collection Tips
- Use a container provided by the testing lab
- Run cold water for 30 seconds before sampling
- Fill container completely
- Label with date, time, and sample location
- Keep cool and deliver promptly to lab
- Consider testing both raw water and after any treatment
Treatment Options for Arsenic Removal
Several effective technologies remove arsenic from drinking water. The best choice depends on your arsenic level, water chemistry, and whether you need point-of-use or whole-house treatment.
What Does NOT Remove Arsenic:
- Boiling water (concentrates arsenic)
- Standard carbon filters (Brita, PUR pitchers)
- Chlorination
- Water softeners alone
Effective Treatment Methods
1. Reverse Osmosis (RO)
- Effectiveness: Removes 90-95% of arsenic (both forms)
- Types: Point-of-use (under-sink) most common
- Cost: $200-600 for under-sink systems
- Pros: Removes many other contaminants, well-proven
- Cons: Produces wastewater, requires filter maintenance
Best for: Most households with arsenic concerns
2. Adsorptive Media (Iron-Based)
- Effectiveness: Removes 95%+ of arsenic when properly designed
- How it works: Iron oxide media binds arsenic
- Types: Point-of-use or whole-house
- Cost: $200-1,500 depending on size
- Pros: No wastewater, works well for arsenate
- Cons: May need pre-oxidation for arsenite
Best for: Moderate levels, whole-house treatment
3. Ion Exchange
- Effectiveness: Removes 90-95% of arsenate (As V)
- Types: Point-of-use or whole-house
- Cost: $500-2,000
- Pros: Effective for arsenate
- Cons: Less effective for arsenite; may need pre-oxidation
Best for: Water with arsenate form, higher volume needs
4. Distillation
- Effectiveness: Removes 95%+ of arsenic
- Types: Countertop units
- Cost: $100-400
- Pros: Very effective, removes many contaminants
- Cons: Slow, energy-intensive, small volume
Best for: Small volumes, backup treatment
Important Considerations
- Know your arsenic form: Arsenite (As III) requires oxidation before some treatments
- Water chemistry matters: pH, iron, and other factors affect treatment
- NSF certification: Look for NSF/ANSI 53 or 58 certification for arsenic
- Post-treatment testing: Test water after installation to confirm effectiveness
- Professional assessment: For high levels or whole-house systems, consult a water treatment professional
Regional Concerns: Where Arsenic Is Most Common
Arsenic contamination is not evenly distributed across the United States. Certain regions have significantly higher natural arsenic levels due to local geology.
High-Risk Regions
Southwestern United States
Arizona, Nevada, New Mexico, and parts of California have some of the highest natural arsenic levels due to arid climate and geology.
Northern New England
Maine, New Hampshire, and Vermont have significant arsenic in bedrock aquifers. Up to 20% of private wells may exceed standards.
Upper Midwest
Parts of Michigan, Wisconsin, and Minnesota have elevated arsenic from glacial deposits and bedrock.
Pacific Northwest
Volcanic regions of Oregon and Washington have naturally occurring arsenic. Idaho also affected.
Appalachian Region
Mining activities have contaminated groundwater in parts of West Virginia, Pennsylvania, and other states.
USGS Arsenic Map
The U.S. Geological Survey maintains detailed maps of arsenic occurrence in groundwater. If you rely on a private well, check your area's risk level and prioritize testing.
Resources:
- USGS arsenic groundwater maps
- State health department well testing programs
- Local geological surveys
- Your state's drinking water program
Frequently Asked Questions
Does boiling water remove arsenic?
No. Boiling actually concentrates arsenic by evaporating water while leaving arsenic behind. Never boil water to reduce arsenic levels.
Will a Brita filter remove arsenic?
No. Standard activated carbon filters (Brita, PUR, refrigerator filters) do not effectively remove arsenic. You need reverse osmosis, adsorptive media, or other specialized treatment.
Is it safe to shower in water with arsenic?
Generally yes. Arsenic is not well absorbed through skin, so bathing and showering in arsenic-contaminated water is not considered a significant exposure route. The primary concern is ingestion.
Can arsenic exposure be reversed?
Once exposure stops, arsenic is eliminated from the body within days to weeks. However, some health effects (particularly cancer risk from long-term exposure) may persist. Early detection and stopping exposure is critical.
Is arsenic in rice related to water arsenic?
Rice absorbs arsenic from soil and water during growth. This is a separate exposure route from drinking water. Both sources should be considered for total arsenic exposure, especially for children who consume significant rice products.
How often should I test my well for arsenic?
Test at least once initially, and every 3-5 years afterward. Test more frequently if you live in a high-arsenic region, after any well work, or if nearby land use changes.
Is bottled water arsenic-free?
FDA limits arsenic in bottled water to 10 ppb, the same as EPA's tap water standard. Bottled water can contain arsenic. If using bottled water to avoid arsenic, look for brands that test and publish results showing very low levels.
Health Disclaimer
This guide is for informational purposes only and does not constitute medical advice. Arsenic is a known human carcinogen with serious health effects. If you have been exposed to arsenic-contaminated water or have health concerns, consult your healthcare provider. For water testing recommendations, contact your local health department or state drinking water program.