July 06, 2026
Arsenic in Drinking Water: Is Your Home at Risk?
Arsenic is naturally present in rock formations across large parts of the United States — and it leaches silently into groundwater with no color, no taste, and no odor. Long-term exposure is linked to bladder, kidney, and skin cancers. Here's how to find out if your home is at risk and what to do about it.
Where Does Arsenic Come From?
Arsenic occurs naturally in geological formations and is released into groundwater as rock weathers over time. Volcanic and sedimentary rock types are particularly arsenic-rich, and the aquifers overlying them can carry significant concentrations. Human activities that elevate arsenic include mining, smelting, and the historical use of arsenic-based pesticides in agriculture.
Geographic hotspots in the U.S. include:
- Southwest — Arizona, Nevada, New Mexico (including Phoenix metro)
- Mountain West — Wyoming, Montana, Idaho
- New England — Maine, New Hampshire, Vermont
- Upper Midwest — Michigan, Wisconsin, Minnesota
- Central Valley, California
Arizona has some of the highest naturally occurring arsenic concentrations in the country. Phoenix metro municipal water is treated for arsenic, but levels are worth verifying in your annual CCR. Well owners in the Southwest: arsenic testing is essential, not optional.
Health Risks of Arsenic Exposure
The International Agency for Research on Cancer (IARC) classifies arsenic as a Group 1 human carcinogen — the highest classification, meaning sufficient evidence exists for carcinogenicity in humans. Long-term exposure to arsenic in drinking water is associated with:
- Bladder cancer (strongest association in the literature)
- Lung and skin cancer
- Characteristic skin lesions (keratosis)
- Kidney cancer
- Cardiovascular disease
- Type 2 diabetes (emerging evidence)
- Developmental effects in children
The EPA's current maximum contaminant level is 10 ppb (parts per billion). Critically, the EPA's own non-enforceable MCLG is 0 ppb — acknowledging there is no known safe level of arsenic exposure. Some states enforce stricter limits: New Jersey's MCL is 5 ppb.
How to Find Out If Your Water Has Arsenic
- Municipal users: Check your annual Consumer Confidence Report. Arsenic is a required reporting parameter. Also check the EWG Tap Water Database by ZIP code.
- Private well users: Order testing from a state-certified laboratory. Standard well panels often don't include arsenic — request it specifically.
- USGS data: The USGS National Water Quality Assessment maps arsenic occurrence in groundwater nationally.
What Removes Arsenic from Drinking Water
Arsenic exists in two primary forms: arsenite (As III) and arsenate (As V). Most home treatment systems target arsenate more effectively. Pre-oxidation (converting As III to As V) improves removal efficiency for some technologies.
| Treatment Technology | Arsenic Removal | Notes |
|---|---|---|
| Reverse Osmosis (RO) | 85–95% (As V); 50–70% (As III) | Most common residential solution; NSF/ANSI 58 |
| Activated Alumina | 90%+ | Specialty media; highly effective for arsenic specifically |
| Iron Oxide / Greensand Media | 90%+ | Used in whole-house point-of-entry applications |
| Distillation | 99%+ | Highly effective; high operating cost |
| Standard carbon filter | Minimal | Not designed for arsenic removal |
| Boiling water | None — worsens it | Concentrates arsenic as water evaporates |
For most homeowners, an NSF/ANSI 58 certified under-sink reverse osmosis system is the most practical and cost-effective solution for arsenic in drinking and cooking water. Browse our arsenic filter options for a full range of treatment approaches.
Arsenic removal efficiency depends on which form is present (As III vs. As V) and the baseline concentration. If your level is above 5 ppb, work with a water treatment professional to select the right system and test the filtered output after installation to confirm performance.
Frequently Asked Questions
Does boiling water remove arsenic?
No — boiling concentrates arsenic by evaporating water while leaving dissolved metals behind. Never boil water to try to reduce arsenic contamination.
Is the 10 ppb EPA arsenic limit safe?
The EPA estimates that water at exactly 10 ppb over a lifetime carries approximately a 1-in-300 increased risk of bladder or lung cancer. Many health advocates argue the limit should be lower. The only truly safe level is zero.
Does a refrigerator filter remove arsenic?
Most standard refrigerator filters are certified only for taste, odor, and chlorine (NSF/ANSI 42) — not arsenic. Check the specific NSF certification of your filter model. Most do not remove arsenic. A dedicated arsenic filter at the drinking tap is more reliable.
Arsenic in Your Water? There's a Filter for That.
Browse NSF-certified arsenic reduction systems — under-sink RO and whole-house media filters.
Arsenic Filters RO Systems