We analyzed tap water quality data for hundreds of cities in California to identify the 25 with the most contaminants exceeding health guidelines. This ranking is based on 2026 data from the EPA and EWG databases.
While all public water systems must meet EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels. The cities below have the widest gap between what's in their water and what's considered safe by modern health standards.
Rankings at a Glance
Corona, California
Corona has 25 contaminants exceeding EWG health guidelines out of 46 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Corona water report →Pleasanton, California
Pleasanton has 23 contaminants exceeding EWG health guidelines out of 43 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Pleasanton water report →Fresno, California
Fresno has 22 contaminants exceeding EWG health guidelines out of 51 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Fresno water report →Anaheim, California
Anaheim has 22 contaminants exceeding EWG health guidelines out of 44 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Anaheim water report →Lake Elsinore, California
Lake Elsinore has 22 contaminants exceeding EWG health guidelines out of 42 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Lake Elsinore water report →Wildomar, California
Wildomar has 22 contaminants exceeding EWG health guidelines out of 42 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Wildomar water report →Compton, California
Compton has 22 contaminants exceeding EWG health guidelines out of 35 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Compton water report →Norwalk, California
Norwalk has 21 contaminants exceeding EWG health guidelines out of 45 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Norwalk water report →Dublin, California
Dublin has 21 contaminants exceeding EWG health guidelines out of 41 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Dublin water report →Livermore, California
Livermore has 21 contaminants exceeding EWG health guidelines out of 41 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Livermore water report →Clovis, California
Clovis has 21 contaminants exceeding EWG health guidelines out of 39 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Clovis water report →Lynwood, California
Lynwood has 21 contaminants exceeding EWG health guidelines out of 36 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Lynwood water report →La Habra Heights, California
La Habra Heights has 21 contaminants exceeding EWG health guidelines out of 34 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full La Habra Heights water report →Manteca, California
Manteca has 21 contaminants exceeding EWG health guidelines out of 33 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Manteca water report →La Crescenta, California
La Crescenta has 20 contaminants exceeding EWG health guidelines out of 43 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full La Crescenta water report →Fullerton, California
Fullerton has 20 contaminants exceeding EWG health guidelines out of 42 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Fullerton water report →Garden Grove, California
Garden Grove has 20 contaminants exceeding EWG health guidelines out of 41 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Garden Grove water report →Santa Ana, California
Santa Ana has 20 contaminants exceeding EWG health guidelines out of 40 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Santa Ana water report →Santa Clarita, California
Santa Clarita has 20 contaminants exceeding EWG health guidelines out of 40 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Santa Clarita water report →Pico Rivera, California
Pico Rivera has 20 contaminants exceeding EWG health guidelines out of 38 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Pico Rivera water report →Pacific Grove, California
Pacific Grove has 20 contaminants exceeding EWG health guidelines out of 37 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Pacific Grove water report →Villa Park, California
Villa Park has 20 contaminants exceeding EWG health guidelines out of 35 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Villa Park water report →Alhambra, California
Alhambra has 19 contaminants exceeding EWG health guidelines out of 40 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Alhambra water report →Irvine, California
Irvine has 19 contaminants exceeding EWG health guidelines out of 38 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Irvine water report →Atascadero, California
Atascadero has 19 contaminants exceeding EWG health guidelines out of 38 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Atascadero water report →What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Bromodichloromethane, Chloroform, Dibromochloromethane. These appear repeatedly across different water systems and regions.
Water quality varies significantly even within the same state, driven by local geology, agricultural activity, and industrial proximity.
Across all ranked cities, 522 contaminant readings exceed EWG health guidelines, but only 25 exceed EPA legal limits. This gap of 497 highlights how legal standards may not fully protect public health — EPA limits haven't been updated for many contaminants in decades.
Full Rankings Table
| Rank | City | State | Detected | Above Guidelines | Above Legal | People Served |
|---|---|---|---|---|---|---|
| 1 | Corona | CA | 46 | 25 | 2 | 168,751 |
| 2 | Pleasanton | CA | 43 | 23 | 2 | 79,871 |
| 3 | Fresno | CA | 51 | 22 | 0 | 545,466 |
| 4 | Anaheim | CA | 44 | 22 | 2 | 341,245 |
| 5 | Lake Elsinore | CA | 42 | 22 | 1 | 165,586 |
| 6 | Wildomar | CA | 42 | 22 | 0 | 4,026 |
| 7 | Compton | CA | 35 | 22 | 0 | 74,877 |
| 8 | Norwalk | CA | 45 | 21 | 1 | 17,790 |
| 9 | Dublin | CA | 41 | 21 | 2 | 98,776 |
| 10 | Livermore | CA | 41 | 21 | 2 | 35,672 |
| 11 | Clovis | CA | 39 | 21 | 0 | 125,722 |
| 12 | Lynwood | CA | 36 | 21 | 0 | 66,967 |
| 13 | La Habra Heights | CA | 34 | 21 | 2 | 5,682 |
| 14 | Manteca | CA | 33 | 21 | 1 | 84,625 |
| 15 | La Crescenta | CA | 43 | 20 | 0 | 32,665 |
| 16 | Fullerton | CA | 42 | 20 | 1 | 141,874 |
| 17 | Garden Grove | CA | 41 | 20 | 1 | 174,226 |
| 18 | Santa Ana | CA | 40 | 20 | 1 | 337,716 |
| 19 | Santa Clarita | CA | 40 | 20 | 1 | 17,154 |
| 20 | Pico Rivera | CA | 38 | 20 | 2 | 40,600 |
| 21 | Pacific Grove | CA | 37 | 20 | 0 | 92,450 |
| 22 | Villa Park | CA | 35 | 20 | 2 | 5,773 |
| 23 | Alhambra | CA | 40 | 19 | 0 | 204,393 |
| 24 | Irvine | CA | 38 | 19 | 0 | 468,941 |
| 25 | Atascadero | CA | 38 | 19 | 2 | 30,457 |
Frequently Asked Questions
What city has the worst tap water in California?
Based on 2026 data, Corona, CA has the most contaminants exceeding EWG health guidelines among the cities we analyzed.
How are cities ranked in this report?
Cities are ranked by the number of contaminants exceeding EWG health guidelines. These guidelines are typically stricter than EPA legal limits and reflect current scientific research on safe exposure levels.
Is my tap water safe if my city isn't on this list?
Not necessarily. Even cities not on this list may have contaminants of concern. We recommend checking your specific water quality using our free water scan tool.
What's the best water filter for contaminated water?
A reverse osmosis (RO) system is the most effective for removing the widest range of contaminants. For whole-home protection, a combination of RO for drinking water and a whole-home filter for showers and baths is recommended.
Related Reports
Data sources: Environmental Working Group (EWG) Tap Water Database, U.S. EPA Safe Drinking Water Information System (SDWIS)
Last updated: March 2026
Methodology: Contaminant levels are compared against both EPA legal limits (Maximum Contaminant Levels) and EWG health guidelines, which are often stricter and based on the latest scientific research.
