California Water Quality
Drinking water data for all 58 counties.
Avg Water Score
44.6
State Grade
D
Counties with Data
58
of 58 total
All California Counties
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Frequently Asked Questions
Which county in California has the best water quality?
San Francisco County has the highest water quality score in California at 86.0/100 (Grade: A), based on EPA SDWIS data.
Which county in California has the most water violations?
Madera County has among the lowest water quality scores in California at 8.8/100. See the individual county page for detailed violation history.
Is the tap water safe to drink in California?
California has an average water quality score of 44.6/100 based on EPA Safe Drinking Water Act compliance data. Individual county scores vary — check your specific county's page for detailed information.
What contaminants are found in California water supplies?
Drinking water quality varies by county and water system. The EPA Safe Drinking Water Information System (SDWIS) tracks violations for contaminants like lead, nitrates, bacteria, and disinfection byproducts. See individual county pages for specific contaminant and violation history.
Data Source
Water quality data sourced from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.
Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.