California Water Report Card: Worst Water Systems
The most contaminated public water systems in California, ranked by PFAS levels, lead, and EPA violations from official EPA data.
Quick Answer
Potrero Elementary School has the highest PFAS in California at 250.2 ppt (63x the EPA limit). Loma Linda University has the highest lead at 216 ppb. The tables below rank the worst systems in each category so you can see how your water compares.
Highest PFAS Levels in California
Public water systems in California with the highest peak PFAS ("forever chemical") reading in EPA UCMR5 testing (2023-2025). The EPA enforceable limit for PFOA and PFOS is 4 ppt.
| # | Water System | Location | Peak PFAS (ppt) | Compounds | vs 4 ppt limit |
|---|---|---|---|---|---|
| 1 | Potrero Elementary School | – | 250.2 | 9 | 63x |
| 2 | Running Springs Water District | Running Springs · 5,268 served | 236.5 | 10 | 59x |
| 3 | Liberty Utilities - Bellflower-Norwalk | – | 59 | 7 | 15x |
| 4 | City Of Atwater | – | 59 | 10 | 15x |
| 5 | Montebello Land & Water Co. | – | 53 | 8 | 13x |
| 6 | Northrop Grumman Corp. | – | 53 | 6 | 13x |
| 7 | Hesperia Wd | Hesperia · 100,744 served | 50.3 | 6 | 13x |
| 8 | City Of Fresno | – | 47 | 10 | 12x |
| 9 | City Of Sacramento Main | Sacramento · 527,979 served | 41.4 | 8 | 10x |
| 10 | City Of Clovis | – | 41 | 9 | 10x |
| 11 | Downey - City, Water Dept. | – | 38 | 7 | 10x |
| 12 | Tract 349 Mutual Water Co. | – | 36.5 | 4 | 9x |
Highest Lead Levels in California
Community water systems in California with the highest 90th-percentile lead result under the EPA Lead and Copper Rule. The EPA action level is 15 ppb; there is no safe level of lead for children.
| # | Water System | Location | Lead 90th-pctile (ppb) | vs 15 ppb |
|---|---|---|---|---|
| 1 | Loma Linda University | Loma Linda · 15,368 served | 216 | 14.4x over |
| 2 | Treasure Island | Burlingame · 3,864 served | 100 | 6.7x over |
| 3 | Pine Valley Mutual Wc | Pine Valley · 2,645 served | 99.4 | 6.6x over |
| 4 | Needles, City Of | Needles · 8,766 served | 46.5 | 3.1x over |
| 5 | Aromas Water District | Aromas · 2,988 served | 26 | 1.7x over |
| 6 | Green Valley Mwc | Green Valley Lake · 2,993 served | 24.9 | 1.7x over |
| 7 | Fallsvale Service Company | Forest Falls · 1,046 served | 23 | 1.5x over |
| 8 | Cedarpines Park Mwc | Cedarpines Park · 2,458 served | 23 | 1.5x over |
| 9 | Lake Arrowhead Csd | Lake Arrowhead · 7,038 served | 22 | 1.5x over |
| 10 | Usmc - 29 Palms | Twentynine Palms · 15,248 served | 20 | 1.3x over |
| 11 | California State Fair | Sacramento · 9,280 served | 16 | 1.1x over |
| 12 | Rincon Del Diablo Mwd (Id-A) | Escondido · 3,275 served | 14 | within |
Most EPA Violations in California
Community water systems in California with the most health-based EPA Safe Drinking Water Act violations on record. A health-based violation means a contaminant exceeded its federal limit or required treatment was not applied.
| # | Water System | Location | Health-based violations |
|---|---|---|---|
| 1 | Us Army Fort Irwin | Fort Irwin · 15,701 served | 60 |
| 2 | Nacimiento Water Company | Bradley · 2,181 served | 22 |
| 3 | Helendale Community Service District | Helendale · 6,347 served | 21 |
| 4 | Indian Hills Camp | Jamul · 13,032 served | 17 |
| 5 | Heritage Ranch Csd | Paso Robles · 2,956 served | 15 |
| 6 | San Joaquin County-Raymus Village | Stockton · 1,086 served | 9 |
| 7 | Pine Valley Mutual Wc | Pine Valley · 2,645 served | 8 |
| 8 | Thousand Trails San Benito Preserve | Paicines · 1,017 served | 6 |
| 9 | California Institution For Men | Chino · 10,667 served | 5 |
| 10 | Little Potato Slough Mutual | Lodi · 1,510 served | 5 |
| 11 | Hollister, City Of | Hollister · 26,017 served | 5 |
| 12 | San Juan Bautista, City Of | San Juan Bautista · 2,335 served | 5 |
How This Report Card Is Built
PFAS rankings use EPA UCMR5 monitoring (2023-2025), showing each system's peak detection above the 4 ppt EPA limit. Lead rankings use the EPA Lead and Copper Rule 90th-percentile tap results. Violation counts come from the EPA Safe Drinking Water Information System (SDWIS) and count health-based violations. Lead and violation lists are limited to community water systems serving 1,000 or more people. Figures are the most severe on record and do not necessarily reflect current treated water.
Frequently Asked Questions
What is the most PFAS-contaminated water system in California?
In EPA UCMR5 testing (2023-2025), Potrero Elementary School had the highest recorded PFAS level in California at 250.2 ppt - about 63x the EPA's 4 ppt limit for PFOA and PFOS.
Which California water system has the highest lead levels?
Loma Linda University in Loma Linda had the highest 90th-percentile lead result in California under the EPA Lead and Copper Rule at 216 ppb - 14.4x the 15 ppb action level.
Which California water system has the most EPA violations?
Us Army Fort Irwin in Fort Irwin has the most health-based EPA Safe Drinking Water Act violations on record in California, with 60 violations.
Where does the California water report card data come from?
PFAS figures come from EPA UCMR5 monitoring (2023-2025), lead from the EPA Lead and Copper Rule 90th-percentile tap results, and violations from EPA SDWIS health-based violation records. Figures are the most severe on record and do not necessarily reflect current treated water. Check your exact address at knowyourexposure.com.
What California Residents Should Do
- Look up your exact address at knowyourexposure.com for your system's data
- See the full California water quality overview
- If your system is listed, a certified filter (reverse osmosis for PFAS, NSF-53 for lead) reduces exposure at the tap. See the best water filters.