Arsenic in Well Water: Testing, Health Risks & Treatment Options
Arsenic is one of the most serious contaminants found in private well water, and California has some of the highest natural arsenic levels in the nation. This comprehensive guide explains where arsenic comes from, the health risks it poses, California's strict 10 ppb standard, how to test your well, and the most effective treatment options available for San Diego County homeowners.
📋 In This Guide
⚠️ Important Health Notice
Arsenic is a known carcinogen with no safe level of exposure. If you suspect arsenic in your well water, stop drinking it immediately and have it tested by a certified laboratory. Use bottled water until you receive results.
What Is Arsenic and Where Does It Come From?
Arsenic is a naturally occurring element found in rocks, soil, and groundwater throughout the world. In California, arsenic contamination in wells is primarily natural—not from pollution—making it particularly challenging because you can't simply remove a contamination source.
Natural Sources of Arsenic
- Volcanic rocks and deposits: Common in California's geological history
- Mineral ore deposits: Arsenic often accompanies gold, copper, and other minerals
- Geothermal areas: Hot springs and geothermal zones concentrate arsenic
- Sedimentary deposits: Ancient marine sediments can contain arsenic
Human-Made Sources
- Historical pesticide use: Lead arsenate was used in orchards until the 1940s
- Mining operations: Historic and current mining can release arsenic
- Industrial contamination: Some manufacturing processes use arsenic
- Wood preservatives: CCA-treated wood (now restricted) contained arsenic
Forms of Arsenic in Water
Arsenic exists in two forms in groundwater, and this matters for treatment:
- Arsenic(V) / Arsenate: More common in oxygen-rich water, easier to remove
- Arsenic(III) / Arsenite: More toxic and harder to remove, may require pre-oxidation
Health Risks of Arsenic Exposure
Arsenic is classified as a Group 1 carcinogen by the World Health Organization. Even low levels of exposure over time can cause serious health effects.
Short-Term (Acute) Exposure
Drinking water with very high arsenic levels can cause:
- Nausea, vomiting, and diarrhea
- Numbness in hands and feet
- Muscle cramps
- In extreme cases, death (rare with drinking water)
Long-Term (Chronic) Exposure
The greater concern for well owners is long-term exposure to lower levels:
- Cancer: Bladder, lung, kidney, liver, and skin cancers
- Cardiovascular disease: Heart disease and stroke
- Diabetes: Increased risk of type 2 diabetes
- Skin changes: Darkening, lesions, and hardening of skin
- Neurological effects: Cognitive impairment, especially in children
- Developmental effects: Low birth weight, developmental delays
Children Are Most Vulnerable
Children who drink arsenic-contaminated water are particularly at risk for developmental problems, lower IQ scores, and immune system effects. If you have children and haven't tested your well for arsenic, do so immediately.
California Arsenic Standards
California has adopted the federal EPA standard for arsenic in drinking water:
Key Numbers to Know
- Maximum Contaminant Level (MCL): 10 parts per billion (ppb) or 0.010 mg/L
- Public Health Goal (PHG): 0.004 ppb (the level with negligible health risk)
- Detection Limit for Purposes of Reporting (DLR): 2 ppb
What this means for private well owners: While the 10 ppb MCL legally applies to public water systems, private well owners are strongly advised to meet the same standard. If your well tests above 10 ppb, treatment is strongly recommended. If it tests above 50 ppb, immediate action is essential.
Testing Your Well for Arsenic
When to Test
- When you buy a property: Always test before closing
- Every 3-5 years: Baseline monitoring for existing wells
- After deepening a well: Different aquifers may have different arsenic levels
- After nearby drilling or construction: Can disturb arsenic deposits
- If neighbors find arsenic: Geological conditions are often similar
How to Get Tested
- Use a certified laboratory: State-certified labs ensure accurate results
- Request proper containers: The lab will provide sample bottles
- Follow collection instructions: Run water 2-3 minutes before sampling
- Request "speciated" analysis: This tells you Arsenic III vs V levels (important for treatment)
- Keep samples cold: Refrigerate until you deliver to lab
Testing Costs
- Basic arsenic test: $25-$50
- Speciated arsenic test: $50-$100
- Comprehensive water quality panel: $150-$300 (includes arsenic plus other contaminants)
Need Water Testing Help?
We can collect samples and coordinate testing with certified laboratories. We'll help you understand your results and recommend appropriate treatment if needed.
Call (760) 440-8520Arsenic Levels in San Diego County
San Diego County has variable arsenic levels depending on location and geology. Here's what we typically see:
| Area | Typical Arsenic Levels | Notes |
|---|---|---|
| Coastal Areas | Generally low (<5 ppb) | Sedimentary geology |
| Mountain/Foothill Areas | Variable (2-25 ppb) | Granite geology, more variable |
| Julian/Cuyamaca | Higher risk (5-30+ ppb) | Mining history, mineral deposits |
| Anza-Borrego Area | Elevated (10-50+ ppb) | Geothermal influence |
| Valley Center/Ramona | Low to moderate (2-15 ppb) | Mixed geology |
Important: These are generalizations. Arsenic levels can vary significantly from well to well, even on neighboring properties. The only way to know your arsenic level is to test.
Treatment Options
Several proven technologies remove arsenic from well water. The best choice depends on your arsenic level, water chemistry, and whether you need whole-house or point-of-use treatment.
1. Adsorptive Media Filters
Best for: Whole-house treatment, moderate arsenic levels (10-50 ppb)
These systems use iron-based media that attracts and holds arsenic as water passes through. They're the most popular whole-house option for residential wells.
- Pros: No wastewater, low maintenance, effective for both As(III) and As(V)
- Cons: Media replacement every 1-3 years, higher upfront cost
- Removal rate: 95-99% effective
- Brands: Bayoxide E33, AdEdge, ArsenX
2. Reverse Osmosis (RO)
Best for: Point-of-use (drinking water only), high effectiveness needed
RO systems force water through a membrane that blocks arsenic and other contaminants. Most effective for As(V); may need pre-oxidation for As(III).
- Pros: Highly effective (95%+), removes other contaminants too, affordable
- Cons: Wastes 3-4 gallons per gallon produced, treats drinking water only
- Removal rate: 95-99% for As(V), lower for As(III) without pre-treatment
3. Ion Exchange
Best for: High arsenic levels, water with low competing ions
Specialized ion exchange resins swap arsenic for harmless chloride ions. Works well for As(V) but requires pre-oxidation for As(III).
- Pros: Very effective, regenerable media
- Cons: Sulfate and nitrate compete for capacity, generates brine waste
- Removal rate: 90-95% under good conditions
4. Oxidation + Filtration
Best for: Water with high As(III), combined iron/arsenic problems
Chlorine or potassium permanganate oxidizes As(III) to As(V) and iron to a filterable form. Arsenic then co-precipitates with iron and is filtered out.
- Pros: Addresses iron and arsenic together, effective for As(III)
- Cons: More complex system, requires iron in water to work well
What Doesn't Work
- Boiling: Concentrates arsenic—makes it WORSE
- Standard carbon filters: Remove taste/odor but NOT arsenic
- Water softeners: Do not remove arsenic
- Sediment filters: Only remove particles, not dissolved arsenic
Treatment Costs
| Treatment Type | Equipment Cost | Installation | Annual Maintenance |
|---|---|---|---|
| Point-of-Use RO | $150-$400 | $100-$200 | $50-$100 (filters) |
| Whole-House RO | $2,000-$5,000 | $500-$1,000 | $200-$500 |
| Adsorptive Media | $1,500-$3,500 | $300-$600 | $300-$800 (media) |
| Ion Exchange | $2,000-$4,500 | $400-$800 | $200-$400 (salt/regen) |
Frequently Asked Questions
What is a safe level of arsenic in well water?
California has set the Maximum Contaminant Level (MCL) for arsenic at 10 parts per billion (ppb), which matches the federal EPA standard. However, there is no truly "safe" level of arsenic—even low levels pose some cancer risk. California's Public Health Goal (PHG), which represents the level with negligible health risk, is just 0.004 ppb. If your well tests above 10 ppb, treatment is strongly recommended.
How do I test my well water for arsenic?
Arsenic testing requires a water sample analyzed by a state-certified laboratory. Home test kits exist but are not reliable for the precision needed at low levels. Collect a sample in a laboratory-provided container, following their instructions carefully. Standard arsenic tests cost $25-$50 and results typically take 5-10 business days. Test when you first buy a property, after any changes to your well, and every 3-5 years for ongoing monitoring—or annually if you're in a high-risk area.
What is the best treatment for arsenic in well water?
The best treatment depends on your arsenic levels and water chemistry. For most residential applications, adsorptive media filters (using iron-based media) are the most cost-effective option for whole-house arsenic removal. Reverse osmosis systems are highly effective at the point-of-use (under sink). Ion exchange systems work well but may be affected by competing contaminants. For high arsenic levels or complex water chemistry, a combination of treatment methods may be needed.
Can boiling water remove arsenic?
No—boiling water does NOT remove arsenic. In fact, boiling concentrates arsenic because water evaporates but arsenic remains behind. This makes boiled water more dangerous, not safer. Unlike bacteria, which boiling kills, arsenic is an element that cannot be destroyed or removed by heat. Only proper filtration methods like reverse osmosis, adsorptive media, or ion exchange can effectively remove arsenic from drinking water.
How much does arsenic treatment cost for a private well?
Point-of-use reverse osmosis systems (treating drinking water only) cost $200-$600 installed. Whole-house adsorptive media systems range from $1,500-$4,000 installed, with media replacement every 1-3 years costing $300-$800. Ion exchange systems run $2,000-$5,000 installed with ongoing regeneration costs. Annual arsenic testing costs $25-$50. Total first-year costs typically range from $500 for basic point-of-use treatment to $5,000+ for comprehensive whole-house systems.
Concerned About Arsenic in Your Well?
Southern California Well Service can help you test your water and recommend the most effective, cost-efficient treatment solution for your specific situation. We serve all of San Diego County.
Call (760) 440-8520
