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 legally required for public water systems and strongly recommended for private wells.

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 arsenic removal, especially for arsenic(V). 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. Professional water testing should guide your treatment choice.

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.

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.