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Arsenic is a naturally occurring element that can contaminate groundwater and poses serious health risks even at low levels. Learn about sources, health effects, and how to protect your family.
Arsenic is a naturally occurring metalloid element found in rocks and soil throughout the world. It exists in two main forms: organic arsenic (less harmful, found in some foods) and inorganic arsenic (highly toxic, found in drinking water and industrial processes).
When groundwater flows through arsenic-rich geological formations, it dissolves the arsenic and carries it into wells and aquifers. This is why arsenic contamination is often a regional problem tied to specific geology rather than human activity.
Critical: Arsenic is a known human carcinogen. Long-term exposure to arsenic in drinking water increases the risk of cancer, even at levels below the current EPA limit.
The more toxic and mobile form. Found in oxygen-poor groundwater conditions. Harder to remove with standard treatment methods.
Typical source: Deep wells, reducing conditions
Less toxic form found in oxygen-rich water. Easier to remove through conventional treatment methods like ion exchange and adsorption.
Typical source: Surface water, shallow wells
Treatment note: Many arsenic removal systems require pre-oxidation to convert arsenite (As III) to arsenate (As V) for effective removal.
Children: More susceptible to neurological effects and may have higher exposure relative to body weight.
Pregnant women: Arsenic crosses the placenta and is associated with low birth weight, preterm birth, and developmental effects.
People with poor nutrition: Deficiencies in certain nutrients may increase arsenic absorption and toxicity.
The highest level of arsenic allowed in public drinking water. This standard was lowered from 50 ppb to 10 ppb in 2001, effective January 2006.
Note: This limit represents a balance between health protection and treatment feasibility, not a "safe" level.
The EPA's health goal for arsenic is zero because arsenic is a known carcinogen with no safe threshold. Any level of exposure carries some cancer risk.
The EPA estimates that drinking water with 10 ppb arsenic over a lifetime increases cancer risk by approximately 1 in 300 - significantly higher than EPA's typical acceptable risk level of 1 in 10,000.
Arsenic occurs naturally in certain rock formations, particularly in the western U.S., New England, and parts of the Midwest. When groundwater contacts these rocks, arsenic dissolves into the water.
Historic and active mining sites, especially copper and gold mines, can release arsenic into groundwater and surface water through mine drainage and tailings.
Historical use of arsenic-based pesticides (especially in orchards) left residual contamination. Some animal feed additives and fertilizers also contain arsenic.
Electronics manufacturing, glass production, wood preservation (CCA-treated lumber), and other industrial processes can release arsenic into water supplies.
Coal contains trace amounts of arsenic. Coal ash from power plants can leach arsenic into groundwater if not properly contained.
Arsenic contamination varies significantly by region due to geological differences. Areas with naturally high arsenic levels include:
Arizona, Nevada, New Mexico - volcanic and mining geology
Parts of Oregon and Washington - volcanic deposits
Maine, New Hampshire - bedrock geology
Parts of Michigan, Wisconsin, Minnesota
San Joaquin Valley agricultural areas
Gulf Coast region and west Texas
Private Wells: About 2.1 million Americans using private wells are estimated to have arsenic levels above 10 ppb. Private wells are not regulated by EPA and require owner testing.
Available at hardware stores and online. These provide a basic yes/no result above/below a threshold (usually 10 or 50 ppb).
Pros: Quick, inexpensive. Cons: Limited accuracy, don't provide exact levels.
Most accurate method. Labs use EPA-approved methods to detect arsenic at very low levels (1-5 ppb detection limits).
Contact your state health department for a list of certified labs, or use the EPA Safe Drinking Water Hotline: 800-426-4791.
Public water systems test for arsenic and report results in annual Consumer Confidence Reports. Search for your city on our site to see reported levels.
Testing Recommendations:
Removes 85-95% of arsenic (both forms). Point-of-use under-sink systems are most practical and cost-effective for drinking water.
Cost: $200-500 for under-sink system + $50-100/year maintenance
Specialized media (like granular ferric hydroxide) binds arsenic as water passes through. Can remove 95%+ of arsenate; less effective for arsenite without pre-oxidation.
Cost: $500-2,000 point-of-entry systems, media replacement every 1-3 years
Strong-base anion exchange resins remove arsenate effectively. Requires pre-oxidation for arsenite. Regeneration produces arsenic-laden waste requiring proper disposal.
Cost: $1,000-3,000 for whole-house systems
Boils water and collects steam, leaving arsenic behind. Removes 98%+ of arsenic but is energy-intensive and produces limited quantities.
Cost: $300-800 for countertop units
Does NOT Remove Arsenic:
Under-Sink Reverse Osmosis
Most DIY-friendly option. Basic plumbing skills required. Filters drinking water at one location.
Countertop Distillers
No installation required. Produces small quantities (1-2 gallons per batch). Good for drinking water only.
Pitcher Filters (Limited)
Very few pitcher filters remove arsenic. Verify NSF 53 certification specifically for arsenic reduction.
Whole-House Treatment
Professional installation of point-of-entry systems. Treats all water in the home.
Cost: $2,000-5,000 including installation
Pre-Oxidation Systems
Converts arsenite to arsenate for better removal. Recommended when arsenite is the dominant form.
Cost: $1,500-4,000 additional
Well Treatment
In some cases, a deeper well or different aquifer may have lower arsenic levels. Consult a hydrogeologist.
Know your arsenic level before choosing treatment. Test annually if using a private well.
Choose NSF 53-certified systems specifically rated for arsenic reduction. Verify the system addresses your arsenic type (III or V).
Replace filters and media on schedule. Arsenic removal capacity decreases over time.
Rice can contain significant arsenic. Vary grain sources and consider rinsing rice before cooking.
Old pressure-treated wood may leach arsenic. Avoid burning it or using it for garden beds.
Health advocates continue to push for lowering the arsenic MCL below 10 ppb. Studies show health effects at levels below the current standard.
Recent studies link even low-level arsenic exposure to increased cardiovascular disease risk, strengthening the case for stricter standards.
New adsorptive media formulations are improving arsenic removal efficiency and reducing costs for point-of-use systems.
Increased attention on private well contamination, with some states offering testing subsidies and treatment assistance programs.
No. Arsenic is completely tasteless, colorless, and odorless at levels found in drinking water. Laboratory testing is the only way to detect it.
No. Boiling actually concentrates arsenic by evaporating water while leaving the arsenic behind. Never boil water to try to remove arsenic.
The primary concern with arsenic is ingestion. Arsenic is not well absorbed through skin, so bathing in water with typical contamination levels is generally not considered a significant risk.
Rice can accumulate arsenic from soil and water. Rinsing rice and cooking in excess water (then draining) can reduce arsenic content by 40-60%. Vary grains to reduce exposure.
In high-risk areas, test annually. Otherwise, test when you move in, after any changes to the well, and every 3-5 years. Arsenic levels can change over time.
Bottled water is regulated to the same 10 ppb standard as tap water. Some spring water sources may contain arsenic. Check with the bottler or choose brands that test below detection limits.
See your city's water quality report and check for arsenic detections in your area.
This information is provided for educational purposes only and is not intended as medical advice. If you are concerned about arsenic exposure, consult with a healthcare provider. Water quality data is sourced from EPA databases and may not reflect the most current testing results. Always verify with your local water utility or conduct independent testing for the most accurate information.