Arsenic
A naturally occurring element found in rock and soil that can dissolve into groundwater.
Source
Natural geological deposits, mining operations, and agricultural runoff.
Health Risk
Long-term exposure linked to skin, bladder, and lung cancer, as well as cardiovascular disease.
Filter Tip
Reverse osmosis is the most effective home treatment for arsenic. Some activated alumina filters also work.
Arsenic is a naturally occurring element found in rock, soil, and groundwater throughout the world. It is one of the most significant drinking water contaminants because of its prevalence and toxicity — the EPA classifies arsenic as a known human carcinogen.
The EPA's Maximum Contaminant Level for arsenic is 10 parts per billion (ppb), set in 2001. The MCLG (health goal) is zero, reflecting the fact that any level of arsenic exposure carries some risk.
Why Is Arsenic Dangerous?
Arsenic is a potent carcinogen even at low levels. Long-term health effects include:
- Skin, bladder, and lung cancer
- Cardiovascular disease and heart problems
- Diabetes
- Skin changes including darkening and thickening
- Nervous system effects including numbness
- Developmental effects in children
How Does Arsenic Get Into Water?
Arsenic enters water primarily through natural geological processes — it dissolves from rock and soil into groundwater. It is particularly common in the western United States, parts of New England, and areas with volcanic rock. Industrial sources include mining, smelting, and agricultural pesticide runoff.
How to Remove Arsenic From Your Water
- Reverse Osmosis: The most effective home treatment, removing 90-95% of arsenic
- Activated Alumina: Effective, especially for arsenate (arsenic V)
- Iron-Based Adsorption: Newer technology that is very effective for arsenic
- Distillation: Effective but slow and energy-intensive
Standard carbon filters are NOT effective for arsenic. Be sure any filter you choose is certified for arsenic removal (NSF/ANSI 53 or 58).
Arsenic Levels in US Cities
Based on verified municipal water quality reports (Consumer Confidence Reports) from 5 cities.
Frequently Asked Questions
What level of arsenic in water is safe?
The EPA MCL is 10 ppb, but the MCLG (health goal) is zero. Any level of arsenic exposure carries some cancer risk. The 10 ppb standard balances health protection with treatment feasibility.
Which states have the most arsenic in water?
Arsenic in groundwater is most common in the western US (Arizona, Nevada, California, Oregon), parts of the Midwest, and portions of New England. It tends to be higher in groundwater systems than surface water.
Does boiling water remove arsenic?
No. Boiling concentrates arsenic as water evaporates, making it worse. Use a reverse osmosis filter or bottled water if your water contains arsenic above the EPA limit.
Related Contaminants
Lead
A toxic heavy metal that typically enters drinking water through corroding pipes, faucets, and solder — not from the water source itself.
Chromium-6 (Hexavalent Chromium)
A toxic form of chromium made famous by the Erin Brockovich case. Can occur naturally or from industrial pollution.
Uranium
A naturally occurring radioactive element found in some groundwater sources.