California Water Systems with Most Unresolved Health-Based Violations — 2026
California community water utilities ranked by open federal health-based drinking water violations in EPA's SDWIS enforcement records, with demographic context from the Census American Community Survey.
ranked
with demographic data
vintage
boundaries (March 2026)
These 48 California water utilities carry the most open federal health-based violations in EPA's enforcement records. Sorted by unresolved count; demographic context from the U.S. Census is shown alongside but is not a ranking input.
| Rank | Water System | State | Pop served | Unresolved health violations | Health viol. (5yr) | % PoC served | % Below 200% FPL | Last violation |
|---|---|---|---|---|---|---|---|---|
| 1 | City of Lindsay | California | 10,929 | 32 | 33 | 86% | 51% | 2025-10-01 |
| 2 | City of Hughson | California | 6,241 | 21 | 21 | 44% | 23% | 2025-07-01 |
| 3 | City of Dos Palos | California | 7,477 | 14 | 14 | 82% | 52% | 2025-07-01 |
| 4 | City of Lemoore | California | 25,315 | 13 | 13 | 63% | 34% | 2025-07-02 |
| 5 | City of Avenal | California | 4,483 | 6 | 6 | 92% | 58% | 2024-10-17 |
| 6 | City of Calistoga | California | 5,264 | 5 | 8 | 45% | 21% | 2025-06-01 |
| 7 | Oildale Mwc | California | 27,600 | 5 | 5 | 44% | 43% | 2024-10-01 |
| 8 | Suisun-Solano Water Authority | California | 28,675 | 3 | 11 | 78% | 24% | 2024-10-17 |
| 9 | Signal Hill - City, Water Department | California | 5,254 | 2 | 5 | 75% | 28% | 2025-04-01 |
| 10 | City of Stockton | California | 178,113 | 2 | 2 | 79% | 33% | 2024-01-01 |
| 11 | Yucaipa Valley Water District | California | 60,758 | 2 | 2 | 45% | 25% | 2024-07-01 |
| 12 | City of Livingston | California | 12,677 | 2 | 2 | 90% | 42% | 2024-10-17 |
| 13 | Winton Water & Sanitary District | California | 8,672 | 2 | 2 | 83% | 43% | 2024-10-17 |
| 14 | Yosemite Spring Park Util Company | California | 3,941 | 1 | 8 | 27% | 22% | 2025-10-06 |
| 15 | East Niles Csd | California | 31,094 | 1 | 3 | 78% | 45% | 2024-10-17 |
| 16 | Scwa - Laguna/Vineyard | California | 145,429 | 1 | 1 | 69% | 19% | 2024-10-17 |
| 17 | City of Fairfield | California | 101,593 | 1 | 1 | 72% | 25% | 2024-10-17 |
| 18 | City of Porterville | California | 48,713 | 1 | 1 | 79% | 49% | 2024-10-17 |
| 19 | City of Los Banos | California | 43,989 | 1 | 1 | 80% | 39% | 2024-10-17 |
| 20 | City of Ceres | California | 36,788 | 1 | 1 | 78% | 39% | 2024-10-17 |
| 21 | City of Calexico | California | 36,151 | 1 | 1 | 98% | 49% | 2024-10-17 |
| 22 | Monterey Park-City, Water Department | California | 34,690 | 1 | 1 | 94% | 35% | 2024-10-17 |
| 23 | City of Sanger | California | 24,321 | 1 | 1 | 75% | 34% | 2024-10-17 |
| 24 | City of Riverbank | California | 23,782 | 1 | 1 | 67% | 32% | 2021-11-01 |
| 25 | San Lorenzo Valley Water District | California | 22,610 | 1 | 1 | 23% | 15% | 2024-10-17 |
| 26 | City of Dinuba | California | 22,497 | 1 | 1 | 89% | 51% | 2024-10-17 |
| 27 | City of Oakdale | California | 21,894 | 1 | 1 | 39% | 24% | 2024-10-17 |
| 28 | City of Norco | California | 19,642 | 1 | 1 | 52% | 15% | 2025-07-01 |
| 29 | City of West Sacramento | California | 17,951 | 1 | 1 | 60% | 31% | 2024-10-17 |
| 30 | Bakman Water Company | California | 15,252 | 1 | 1 | 82% | 35% | 2024-10-17 |
| 31 | City of Imperial | California | 13,335 | 1 | 1 | 89% | 33% | 2024-10-17 |
| 32 | City of Parlier | California | 12,388 | 1 | 1 | 97% | 58% | 2024-10-17 |
| 33 | City of Tehachapi | California | 12,224 | 1 | 1 | 45% | 25% | 2024-10-17 |
| 34 | City of Anderson | California | 10,358 | 1 | 1 | 26% | 35% | 2024-10-17 |
| 35 | Arvin Community Services District | California | 9,637 | 1 | 1 | 96% | 64% | 2024-10-17 |
| 36 | City of Orange Cove | California | 7,563 | 1 | 1 | 95% | 58% | 2024-10-17 |
| 37 | City of Farmersville | California | 7,495 | 1 | 1 | 84% | 57% | 2024-10-17 |
| 38 | Earlimart PUD | California | 7,202 | 1 | 1 | 98% | 58% | 2024-10-17 |
| 39 | Yreka, City of | California | 6,610 | 1 | 1 | 22% | 43% | 2024-10-17 |
| 40 | City of Fort Bragg | California | 6,417 | 1 | 1 | 33% | 40% | 2024-10-17 |
| 41 | City of Gridley | California | 6,034 | 1 | 1 | 41% | 39% | 2024-10-17 |
| 42 | Awa, Ione | California | 5,156 | 1 | 1 | 34% | 15% | 2024-12-01 |
| 43 | Folsom State Prison | California | 5,008 | 1 | 1 | 85% | 0% | 2024-10-17 |
| 44 | Solvang Water Division | California | 4,913 | 1 | 1 | 28% | 15% | 2024-03-27 |
| 45 | City of Gustine | California | 4,752 | 1 | 1 | 70% | 39% | 2024-10-17 |
| 46 | Ivanhoe Public Utility District | California | 4,086 | 1 | 1 | 88% | 47% | 2024-10-17 |
| 47 | Bear Valley Csd | California | 4,007 | 1 | 1 | 31% | 24% | 2024-10-17 |
| 48 | Slvwd - Felton Water System | California | 3,530 | 1 | 1 | 23% | 16% | 2025-09-01 |
How to read this ranking
Each row links to a full utility profile with violation history, lead testing results, and service-area ZIPs. The demographic context columns are from independent data sources (ACS, not EJScreen) and are provided for readers who want to examine equity patterns alongside the operational data.
See the full methodology for calculation details, data vintages, and known limitations.
Frequently asked questions
What is an unresolved health-based violation?
A violation of a federal Safe Drinking Water Act standard (Maximum Contaminant Level, Treatment Technique, or Monitoring requirement for a health-based contaminant) that has not been formally returned to compliance in EPA records. These reflect ongoing public-health concerns documented in EPA's ECHO enforcement database.
Why show demographic context next to violations?
Federal Safe Drinking Water Act data does not distinguish between communities by race or income — violations are violations regardless of who is served. We publish demographic columns so readers can independently examine whether specific systems with long-running violations also serve disproportionately low-income or non-white populations. We do not claim causation; we report two independent facts side by side.
Are these the most dangerous water systems in the country?
Not necessarily. "Unresolved" counts procedural and technical violations alongside contaminant exceedances. A high count indicates a system that federal regulators have flagged repeatedly without resolution. For any specific system, click through to its profile page for the individual violations on record.
Where does the data come from?
Violation records come from EPA's Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database, refreshed weekly. Demographic context comes from the U.S. Census American Community Survey (ACS) 5-year estimates (2019-2023), aggregated from block-group level to utility-level using EPA's Community Water System Service Area Boundaries v3 population weights.
ZipCheckup is an independent public-data tool. We are a referral service and do not provide water testing, remediation, or utility services. Rankings reflect publicly-available federal data and are provided for informational purposes. For issues with your specific water system, contact your local water utility or state drinking water program.