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 |
|---|---|---|---|---|
|
Imperial Lakes Inc. Imperial County |
40 | 2 | 0 | |
|
J R Simplot Company Fresno County |
40 | 1 | 0 | |
|
Hilton Mutual Water Company Sonoma County |
36 | 1 | 0 | |
|
Cold Springs Subdivision Cold Springs Rancheria · County |
35 | 8 | 3 | |
|
Madrona Manor Sonoma County |
34 | 2 | 0 | |
|
Costanoa Campground San Mateo County |
33 | 1 | 0 | |
|
UC Desert Research and Extension Center Imperial County |
33 | 2 | 0 | |
|
Haykingdom, Inc. Imperial · Imperial County |
32 | 2 | 1 | |
|
Iid North End Consolidation Imperial County |
30 | 2 | 1 | |
|
Santa Clara Resources Ventura County |
30 | 1 | 0 | |
|
Lockheed Martin Space Systems Santa Cruz County |
28 | 4 | 1 | |
|
Pine Hill Terrace Mobile Home Park Sonoma County |
27 | 1 | 0 | |
|
Park Investments Water System Tulare County |
26 | 1 | 0 | |
|
Garden Court WS #01 Monterey County |
25 | 1 | 0 | |
|
Moreton Bay Professional Plaza Santa Barbara County |
25 | 6 | 1 | |
|
Nps Death Valley, Stovepipe Wells Inyo County |
25 | 1 | 0 | |
|
Tule River Apple Valley County |
25 | 3 | 0 | |
|
Foothill Municipal Water Dist. Los Angeles County |
0 | 2 | 0 |
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.