California Water Quality Report: 2,690 Water-System Violations Mapped to 1,479 ZIPs
2,704 water systems · 1,479 ZIP codes · 2,690 violations
Data: EPA Safe Drinking Water Information System (SDWIS), EPA ECHO
ZipCheckup tracks EPA drinking-water compliance for 2,704 public water systems serving 1,479 ZIP codes in California. The state record shows 2,690 EPA violations, 1,138 health-based.
City Water Quality Map: California
Each circle represents a city. Size indicates population, color indicates water quality grade. Tap a circle for details.
Cities with Most Violations in California
| # | City | Grade | Violations | Systems | Population | |
|---|---|---|---|---|---|---|
| 1 | Santa Maria | 59 | 7 | 145,186 | Details → | |
| 2 | Bakersfield | 52 | 18 | 589,959 | Details → | |
| 3 | Corona | 51 | 11 | 262,651 | Details → | |
| 4 | Riverside | 47 | 10 | 443,626 | Details → | |
| 5 | Norco | 45 | 4 | 25,268 | Details → | |
| 6 | Morongo Valley | 43 | 5 | 3,907 | Details → | |
| 7 | Valley Center | 42 | 5 | 20,596 | Details → | |
| 8 | Pauma Valley | 42 | 5 | 1,693 | Details → | |
| 9 | Pala | 42 | 5 | 1,449 | Details → | |
| 10 | Porterville | 41 | 5 | 80,581 | Details → |
Most Common Contaminants in California
| Contaminant | Category | Violations | ZIPs Affected | Health Risk |
|---|---|---|---|---|
| Lead and Copper Rule Revisions | Treatment Technique | 574 | 225 | Yes |
| Nitrate | Inorganic | 465 | 141 | Yes |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 291 | 131 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 243 | 128 | Yes |
| Lead and Copper Rule | Treatment Technique | 182 | 153 | No |
| Arsenic | Inorganic | 153 | 33 | Yes |
| Combined Uranium | Radionuclides | 125 | 8 | Yes |
| Selenium | Inorganic | 63 | 12 | Yes |
| Surface Water Treatment Rule | Treatment Technique | 61 | 53 | Yes |
| E. coli | Microbiological | 43 | 38 | No |
Water Quality Overview
California has 2,704 community water systems represented across 1,479 directly mapped ZIP records. The associated city records cover approximately 39,426,086 people. The available records contain 2,690 EPA violations, including 1,138 health-based violations.
Health-based violations account for 42% of all violations in California. These violations indicate contaminant levels that may pose direct risks to human health, as opposed to monitoring or reporting failures.
Violation Breakdown
| Violation Type | Count | Percentage |
|---|---|---|
| Health-based | 1,138 | 42.3% |
| Monitoring/Reporting | 1,552 | 57.7% |
| Total | 2,690 | 100% |
Health-based violations are MCL, MRDL (disinfectant) and treatment-technique violations. Monitoring violations indicate failures to test or report - these do not necessarily mean unsafe water, but they mean the water was not properly verified.
Cities with Most Violations
The following cities in California have the highest number of EPA violations:
| Rank | City | Violations | Water Systems | Population |
|---|---|---|---|---|
| 1 | Santa Maria | 59 | 7 | 145,186 |
| 2 | Bakersfield | 52 | 18 | 589,959 |
| 3 | Corona | 51 | 11 | 262,651 |
| 4 | Riverside | 47 | 10 | 443,626 |
| 5 | Norco | 45 | 4 | 25,268 |
| 6 | Morongo Valley | 43 | 5 | 3,907 |
| 7 | Valley Center | 42 | 5 | 20,596 |
| 8 | Pauma Valley | 42 | 5 | 1,693 |
| 9 | Pala | 42 | 5 | 1,449 |
| 10 | Porterville | 41 | 5 | 80,581 |
Violation counts are cumulative across all water systems serving each city. Higher counts may reflect larger systems with more monitoring requirements, not necessarily worse water quality.
Violation Trend Over Time
Year-by-year EPA violations recorded across all water systems in California:
| Year | Health-based violations |
|---|---|
| 2021 | 92 |
| 2022 | 117 |
| 2023 | 208 |
| 2024 | 338 |
| 2025 | 122 |
| 2026 | 16 |
Health-based violations have decreased from 92 in 2021 to 16 in 2026, suggesting improving compliance across California.
Most Common Contaminants
The following contaminants have caused the most violations across California water systems:
| Contaminant | Category | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|
| Lead and Copper Rule Revisions | Treatment Technique | 574 | 225 | Yes |
| Nitrate | Inorganic | 465 | 141 | Yes |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 291 | 131 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 243 | 128 | Yes |
| Lead and Copper Rule | Treatment Technique | 182 | 153 | No |
| Arsenic | Inorganic | 153 | 33 | Yes |
| Combined Uranium | Radionuclides | 125 | 8 | Yes |
| Surface Water Treatment Rule | Treatment Technique | 61 | 53 | Yes |
| E. coli | Microbiological | 43 | 38 | No |
| Consumer Confidence Rule | Reporting | 41 | 35 | No |
How to Check Your Water in California
Enter your ZIP code on ZipCheckup for detailed water-system data including contaminant levels and violation history; the separate Home Safety Score is a multi-source index
Request your CCR - every water utility must provide an annual Consumer Confidence Report
Get a home test - certified kits ($20-$50) or professional lab tests ($150-$400)
Consider filtration - NSF-certified filters can address specific contaminants found in your area
EPA Enforcement
The EPA and state regulators have taken enforcement actions against water systems in California. Enforcement actions range from compliance assistance to formal orders and penalties.
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Enforcement: EPA ECHO
Updated daily.
What are EPA violations?
Health-based violations are EPA violations of a Maximum Contaminant Level (MCL), a Maximum Residual Disinfectant Level (MRDL) or a required treatment technique - the enforceable standards designed to protect human health. California has 1,138 such violations across its water systems. Not all violations cause illness; review each violation type and duration to understand possible health implications.
Understanding water quality grades
ZipCheckup grades water systems from A to F based on EPA violation history, contaminant levels, and system compliance. Grades summarize ZipCheckup's scoring inputs; review the underlying records for specific issues. Grades are calculated per ZIP code and aggregated at the city, county, and state level.
Wondering about your tap water?
Water quality varies by ZIP code. Enter yours to see contaminant data, violations, and filtration recommendations specific to your area.
Check Your ZIP Code Water Quality →Frequently Asked Questions
Is the tap water safe to drink in California?
Records for 2,704 community water systems mapped to ZIPs in California show 2,690 reported violations, including 1,138 health-based. Water quality varies by city and ZIP code - check your specific location for detailed results.
How many violations are on record for water systems serving California?
California has 2,690 EPA violations on record across 1,479 ZIP codes; 1,138 are classified as health-based violations. The remainder are monitoring or reporting violations.
Which city in California has the worst water quality?
Santa Maria, CA has the most recorded EPA violations (59) among the cities with mapped water systems in California in our data. Check your water supplier's report and test your tap water for the most accurate picture of your local water quality.
Which city in California has the best water quality?
Violation records vary by water system across California. Check individual city reports for details.
What contaminants are found in California drinking water?
EPA regulates over 90 drinking-water contaminants nationally; water systems in California monitor those applicable to each system, which can include lead, copper, nitrate, disinfection byproducts, and bacteria. The most common violations vary by region - check your ZIP code for contaminant-specific data.