Arsenic in California Drinking Water — 300 ZIPs Tested

Arsenic Contamination in California

ZipCheckup analyzed drinking water data across 2,630 ZIP codes in California for arsenic contamination. 300 ZIP codes have reported arsenic detections, and 248 have EPA violations on record.

The violation rate for arsenic in California is 9.4% of all ZIP codes — higher than the national average.

EPA Standard for Arsenic

The EPA maximum contaminant level (MCL) for arsenic is 10 ppb, governed by the Arsenic Rule (2006). Water systems that exceed this limit must take corrective action and notify consumers.

Worst ZIP Codes for Arsenic in California

These ZIP codes reported the highest arsenic levels in California based on CCR reports and EPA data:

Lowest Arsenic Levels in California

These ZIP codes had the lowest reported arsenic detections in California:

Health Effects of Arsenic

Long-term exposure to arsenic in drinking water increases the risk of skin, bladder, lung, and kidney cancer. It also causes cardiovascular disease, diabetes, and skin lesions. The EPA classifies arsenic as a Group A human carcinogen.

How to Remove Arsenic From Drinking Water

The most effective treatment for arsenic removal is Reverse Osmosis. Look for filters certified under NSF 53 / NSF 58 standards.

Check Your ZIP Code

Use the ZipCheckup water quality search to see arsenic data for your specific water system in California.