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 |
|---|---|---|---|---|
|
Bridgeport Pud Mono County |
374 | 3 | 1 | |
|
Washington Water District Nevada County |
330 | 3 | 1 | |
|
San Lucas County Water District Monterey County |
315 | 1 | 0 | |
|
Pine Mountain Mutual Water Co. Mendocino County |
310 | 2 | 1 | |
|
Richard A. McGee Training Center Sacramento County |
300 | 1 | 0 | |
|
Spreckels Sugar Company Imperial County |
300 | 4 | 2 | |
|
Usmc/mtn Warfare Trng Ctr Bridgeport Mono County |
300 | 1 | 0 | |
|
Pond School Water System Kern County |
250 | 2 | 1 | |
|
Ramona Oaks RV Resort San Diego County |
250 | 4 | 0 | |
|
Shanel Tribal Utility District County |
250 | 3 | 0 | |
|
Fcsa 30 EL Porvenir Fresno County |
241 | 1 | 0 | |
|
Cacheville Service Dist Yolo County |
239 | 8 | 1 | |
|
Howonquet Community(smith River) Howonquet Community · County |
220 | 5 | 0 | |
|
Cold Springs Main Cold Springs Rancheria · County |
209 | 7 | 2 | |
|
Santa Rosa Reservation County |
205 | 1 | 0 | |
|
Castlewood Mobile Home Park Yuba County |
200 | 1 | 0 | |
|
Improvement District No. 1 Tulare County |
200 | 1 | 0 | |
|
Loma Rica Water Company Yuba County |
200 | 1 | 0 | |
|
Madera CO Md1-Hidden Lake Estates Madera County |
162 | 1 | 0 | |
|
Fairway Mutual Water CO Tulare County |
150 | 1 | 0 | |
|
Grindstone Rancheria County |
150 | 9 | 4 | |
|
Nps Death Valley, Furnace Creek Inyo County |
150 | 1 | 0 | |
|
Madera CO SA16 Sumner Hill Madera County |
135 | 2 | 0 | |
|
San Antonio Canyon Msc San Bernardino County |
119 | 1 | 0 | |
|
Coarsegold Market Madera County |
115 | 2 | 1 | |
|
Guatay Mutual Benefit Corporation San Diego County |
100 | 4 | 1 | |
|
Pit River Montgomery Creek Rancheria Montgomery Creek Rancheria · County |
90 | 11 | 0 | |
|
Fort Bidwell Reservation County |
88 | 6 | 0 | |
|
Nps Death Valley, Cow Creek/nevares Inyo County |
88 | 2 | 0 | |
|
H & J Water Company San Diego County |
86 | 1 | 0 | |
|
Mulberry Union School Imperial County |
85 | 2 | 0 | |
|
Valley Ford Water Association Sonoma County |
84 | 3 | 1 | |
|
Dhs Border Patrol Hwy 94 Checkpoint San Diego County |
83 | 2 | 1 | |
|
Penn Valley Shopping Center Nevada County |
82 | 2 | 0 | |
|
Victor Valley Wastewater Reclam San Bernardino County |
80 | 2 | 0 | |
|
Tulare County Road Yard 2/3 Tulare County |
75 | 1 | 0 | |
|
Gsa Tecate Port of Entry San Diego County |
70 | 1 | 0 | |
|
Turner Trailer Park County |
70 | 7 | 1 | |
|
Toledo MHP County |
68 | 5 | 3 | |
|
Enza Zaden Research San Benito County |
65 | 2 | 0 | |
|
Pit River XL Rancheria Pit River Tribe · County |
61 | 6 | 0 | |
|
Rebel Ridge Village Yuba County |
60 | 1 | 0 | |
|
River Grove Mutual Water Assn Santa Cruz County |
54 | 3 | 0 | |
|
Brandt Cattle Imperial County |
50 | 3 | 1 | |
|
Cascadel Mutual Water System Madera County |
50 | 1 | 0 | |
|
Castle Mountain Mine San Bernardino County |
50 | 3 | 1 | |
|
Meadowbrook Oaks Butte County |
50 | 4 | 2 | |
|
Venture Estates Mwc San Benito County |
50 | 1 | 0 | |
|
Allied Waste of Imperial Valley Imperial County |
45 | 2 | 1 | |
|
Darr Water CO San Bernardino County |
43 | 4 | 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.