Mercury violations in California
25 active public water systems in California had a Mercury violation in the past three years. What Mercury is and why it matters.
Health effects: Chronic exposure to inorganic mercury in water primarily damages the kidneys. Neurological effects — tremors, memory loss, cognitive impairment — are more associated with organic mercury (methylmercury) than with the inorganic form regulated in drinking water. Developing fetuses and young children are most vulnerable.
Systems with a Mercury violation
Latest quarter first, then largest first| System | Serves | Status | Rules violated, 3 yr | Unresolved |
|---|---|---|---|---|
|
Corona, City of Corona · Riverside County |
169,380 | 6 | 0 | |
|
City of Sunnyvale Sunnyvale · Santa Clara County |
157,566 | 5 | 0 | |
|
Norco, City of Norco · Riverside County |
25,068 | 5 | 0 | |
|
Quechan Casino Resort County |
2,950 | 6 | 0 | |
|
Richgrove Community Services District Tulare County |
1,617 | 8 | 3 | |
|
Lakeside Park Association El Dorado County |
924 | 5 | 1 | |
|
Madison Service Dist Yolo County |
876 | 8 | 1 | |
|
Coyote Valley System County |
850 | 5 | 0 | |
|
Madera MH & RV Park Madera County |
450 | 5 | 0 | |
|
Havasu Water Company County |
361 | 11 | 4 | |
|
Sharondale Mesa HOA Riverside County |
340 | 3 | 0 | |
|
Cacheville Service Dist Yolo County |
239 | 8 | 1 | |
|
Melody Woods Water Company Santa Clara County |
168 | 3 | 0 | |
|
Foster Road Mutual Water Company Santa Barbara County |
150 | 4 | 0 | |
|
Kinecta Fcu Santa Barbara County |
104 | 4 | 0 | |
|
Round Valley Admin. Complex County |
100 | 6 | 1 | |
|
Pit River Montgomery Creek Rancheria Montgomery Creek Rancheria · County |
90 | 11 | 0 | |
|
John Hovannisian Water System Madera County |
80 | 8 | 1 | |
|
Gold Rock Ranch Imperial County |
45 | 5 | 0 | |
|
Sws Land Development INC Madera County |
35 | 4 | 0 | |
|
Kyburz Mutual Water Company El Dorado County |
30 | 5 | 0 | |
|
Eastin Stanislaus County |
26 | 2 | 0 | |
|
Moreton Bay Professional Plaza Santa Barbara County |
25 | 6 | 1 | |
|
Santa Ynez Roblar Mobile Home Park Santa Barbara County |
25 | 4 | 0 | |
|
Silverfork School El Dorado County |
25 | 8 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Mercury, including monitoring and reporting lapses. Rules violated and status in the table are for the whole system, not Mercury 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.