Skip to content
FilterScored

Water quality

California water quality

According to the Environmental Working Group (EWG) and the California State Water Resources Control Board, the most commonly flagged contaminants in California drinking water include arsenic, nitrate, uranium, total trihalomethanes, and PFAS. EWG analysis found 177 California water systems serving more than 18.9 million people detected PFAS above the EPA's health-protective limits between 2023 and 2025. Most large public systems meet federal legal standards, but naturally occurring and agricultural contaminants are a documented concern in parts of the state.

Documented considerations

PFAS

According to EWG, 177 California water systems serving roughly 18.9 million people - about half the state's population - detected PFAS above EPA health-protective limits between 2023 and 2025.

Arsenic

According to USGS California GAMA groundwater studies, arsenic occurs naturally in San Joaquin Valley aquifers and was among the constituents most often found above regulatory benchmarks in domestic-supply groundwater.

Nitrate

According to USGS sampling cited in California GAMA studies, nitrate was detected in roughly 97 percent of wells sampled across the San Joaquin Valley, driven largely by synthetic fertilizer and animal manure on cropland.

Uranium

According to State Water Board data summarized by EWG, uranium affected dozens of utilities, often co-occurring with arsenic and nitrate in Central Valley groundwater.

EPA compliance snapshot

From the EPA ECHO Safe Drinking Water Act database, California community water systems carrying one or more violations on record:

1,716
systems with a violation on record
122
with a health-based violation
10
flagged serious violators

Most common violation categories

  • Lead and Copper Rule Revisions (207)
  • Revised Total Coliform Rule (203)
  • Nitrate (129)
  • Lead and Copper Rule (100)
  • TTHM (30)
  • Arsenic (28)

Counts are public EPA ECHO figures. 'Health-based' means a system carries at least one health-based violation flag in ECHO. A violation on record is not a statement that current tap water is unsafe; most systems return to compliance. Always check your utility's Consumer Confidence Report for current status. Source: EPA ECHO, retrieved 2026-06-01.

Certified filters for California's main concerns

FAQ

Is California tap water safe to drink?
Most large California water systems meet federal Safe Drinking Water Act standards. However, according to EWG and the State Water Resources Control Board, some systems, particularly smaller and rural Central Valley systems, have documented detections of arsenic, nitrate, uranium, or PFAS, so residents in affected areas may want to check their utility's Consumer Confidence Report.
Should I worry about PFAS in California water?
According to EWG analysis, 177 California systems serving about 18.9 million people detected PFAS above EPA health-protective limits between 2023 and 2025. Residents can review their water provider's testing data and consider a filter certified for PFAS reduction if their system reports detections.
Why is nitrate a concern in the Central Valley?
According to USGS GAMA groundwater studies, nitrate was detected in about 97 percent of San Joaquin Valley wells sampled, largely from agricultural fertilizer and animal manure, which is a particular concern for households on private wells.

Sources

  1. EWG - PFAS in California Drinking Water Supplies
  2. California State Water Board - PFAS in Drinking Water
  3. California State Water Board - Nitrates in Drinking Water
  4. USGS - Groundwater quality in the San Joaquin Valley (GAMA)

Not sure how to read your local report? See our guide on reading a water quality report.