TTHM (Total Trihalomethanes) violations in California
118 active public water systems in California had a TTHM (Total Trihalomethanes) violation in the past three years, 4 of them in the latest quarter of EPA's data. What TTHM (Total Trihalomethanes) is and why it matters.
Systems with a TTHM (Total Trihalomethanes) violation
Latest quarter first, then largest first| System | Serves | Status | Rules violated, 3 yr | Unresolved |
|---|---|---|---|---|
|
Lindsay, City of Lindsay · Tulare County |
12,659 | 1 | 0 | |
|
City of Dos Palos Dos Palos · Merced County |
7,452 | 2 | 1 | |
|
Havasu Water Company County |
361 | 11 | 4 | |
|
Chemeketa Park Mutual Water Company Santa Clara County |
346 | 1 | 0 | |
|
Yucaipa Valley Water District San Bernardino County |
52,202 | 3 | 0 | |
|
Oildale Mwc Kern County |
45,315 | 2 | 1 | |
|
Suisun-Solano Water Authority Solano County |
29,105 | 2 | 1 | |
|
Lemoore, City of Lemoore · Kings County |
27,185 | 3 | 1 | |
|
Hollister, City of Hollister · San Benito County |
26,598 | 1 | 0 | |
|
Norco, City of Norco · Riverside County |
25,068 | 5 | 0 | |
|
Exeter, City of Exeter · Tulare County |
11,169 | 1 | 0 | |
|
Mammoth Cwd Mono County |
8,234 | 1 | 0 | |
|
Imperial Valley College Imperial County |
7,650 | 1 | 0 | |
|
Castroville Community Services District Monterey County |
7,515 | 2 | 0 | |
|
Northrop Grumman Corp. Los Angeles County |
5,764 | 1 | 0 | |
|
Running Springs Water District San Bernardino County |
5,268 | 1 | 0 | |
|
Stallion Springs Csd Kern County |
4,910 | 2 | 1 | |
|
Idyllwild Water District Riverside County |
3,762 | 2 | 0 | |
|
Forestville Water District Sonoma County |
3,717 | 1 | 0 | |
|
Big River Development Big River · County |
3,550 | 9 | 4 | |
|
Buena Vue Casino County |
3,150 | 1 | 0 | |
|
Quechan Casino Resort County |
2,950 | 6 | 0 | |
|
Pixley Public Util Dist Tulare County |
2,772 | 1 | 0 | |
|
Calif State Polytechnical Univ Pomona Los Angeles County |
2,668 | 2 | 1 | |
|
Tule River Reservation Main Tule River Reservation · County |
2,560 | 9 | 2 | |
|
Clearlake Oaks County Water District Lake County |
2,359 | 1 | 0 | |
|
Westmorland, City of Westmorland · Imperial County |
2,202 | 3 | 1 | |
|
Redding Rancheria County |
2,015 | 7 | 2 | |
|
Cabazon Water District Riverside County |
1,900 | 2 | 0 | |
|
Inyo County Pwd Lone Pine Inyo County |
1,835 | 4 | 1 | |
|
Richgrove Community Services District Tulare County |
1,617 | 8 | 3 | |
|
San Miguelito Mwc San Luis Obispo County |
1,600 | 1 | 0 | |
|
Bear River/singley Hill County |
1,530 | 4 | 0 | |
|
Hydesville Co. W.d. Humboldt County |
1,389 | 3 | 1 | |
|
Sbdno County Service Area 70 Cedar Glen San Bernardino County |
1,240 | 1 | 0 | |
|
Inyo County Pwd Independence Inyo County |
1,108 | 3 | 2 | |
|
Santa Rosa Rancheria Santa Rosa Rancheria · County |
1,000 | 5 | 1 | |
|
Juniper Riviera Cwd San Bernardino County |
858 | 2 | 1 | |
|
Scotia Csd Humboldt County |
681 | 4 | 1 | |
|
Bear River Tish Non Village Bear River - Tish Non Village · County |
650 | 2 | 0 | |
|
Sunbeam Lake RV Resort Imperial County |
650 | 2 | 1 | |
|
Chiriaco Summit Water Dist. Riverside County |
544 | 1 | 0 | |
|
Cazadero Water Company, Inc. (puc) Sonoma County |
525 | 3 | 2 | |
|
Konocti Harbor Resort Lake County |
505 | 1 | 0 | |
|
Alturas Desert Rose Casino Alturas · County |
464 | 2 | 1 | |
|
Usmc Housing Coleville Mono County |
424 | 3 | 0 | |
|
Big Sandy Rancheria Big Sandy Rancheria · County |
408 | 5 | 2 | |
|
Forest Park Mwc San Bernardino County |
406 | 3 | 1 | |
|
Butte Creek Estates Mutual Water CO Butte County |
399 | 3 | 0 | |
|
South Kaweah Mutual Water Company Tulare County |
384 | 3 | 1 |
About this data
A system is counted once if any of its violations in the past three years involved TTHM (Total Trihalomethanes), including monitoring and reporting lapses. Rules violated and status in the table are for the whole system, not TTHM (Total Trihalomethanes) alone.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The California records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet.