California faces unique water quality challenges due to its diverse geography, agricultural industry, and recurring droughts. The state's water supply comes from a complex system of reservoirs, aqueducts, and groundwater basins that serve over 39 million residents. Water quality varies significantly across the state, with some communities facing serious contamination issues while others enjoy excellent tap water.

Based on our analysis of 193 cities in California, the average water quality score is 80/100. 35 cities have water quality scores below 70, indicating potential concerns that residents should be aware of. The highest-rated city is Alameda with a score of 44/100, while Anaheim has the most room for improvement at 98/100.

Water Sources in California

California draws water from multiple sources including the Sierra Nevada snowpack, the Colorado River, local groundwater aquifers, and desalination plants. The State Water Project and Central Valley Project transport water across hundreds of miles. Groundwater provides approximately 40% of the state's water supply during normal years and up to 60% during droughts.

Common Water Contaminants in California

These contaminants have been detected in various California water systems

1Arsenic (naturally occurring in groundwater)

2Nitrates (agricultural runoff)

3Chromium-6 (industrial pollution)

41,2,3-Trichloropropane (legacy pesticide contamination)

5PFAS (emerging contaminants)

6Disinfection byproducts (chlorine treatment residue)

California Water Regulations

California often sets stricter water quality standards than federal EPA requirements. The State Water Resources Control Board oversees drinking water programs, and California has been a leader in establishing standards for emerging contaminants. The state's Proposition 65 requires disclosure of chemicals known to cause cancer or reproductive harm.

Health Considerations

Central Valley communities face particular challenges with nitrate contamination from agricultural activities. Some disadvantaged communities rely on contaminated groundwater without access to treatment. Wildfire ash can temporarily affect water quality in affected watersheds. Lead in older pipes remains a concern in some urban areas.

Recommendations for California Residents

California residents should review their annual Consumer Confidence Reports, consider whole-house filtration in areas with known contamination, and support local water infrastructure investments. Reverse osmosis systems are effective against most California contaminants including arsenic and chromium-6.

Frequently Asked Questions About California Water Quality

Is California's tap water safe to drink?

Most California cities have tap water that meets EPA safety standards. With an average score of 80/100 across 193 cities we analyzed, California generally has good water quality. However, water quality varies by location, so check your specific city's report.

What are the main water quality concerns in California?

The most common water quality concerns in California include arsenic (naturally occurring in groundwater), nitrates (agricultural runoff), chromium-6 (industrial pollution). These contaminants can come from natural sources, industrial activities, or aging infrastructure. Review your city's specific report to see which contaminants affect your area.

Should I use a water filter in California?

Whether you need a water filter depends on your specific location and health concerns. With 35 cities in California showing elevated contaminant levels, residents in those areas may benefit from filtration. Look for filters certified by NSF/ANSI to remove the specific contaminants found in your area.

Where can I find my California water quality report?

Public water systems in California are required to provide annual Consumer Confidence Reports (CCRs) to residents. You can usually find your report on your water utility's website, request it by phone, or access it through the EPA's database. Our city-level reports above summarize key information from these official sources.

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