EPA system CA1910033 · California

California Water Service Co. - Dominguez: Lithium at or above EPA's 10 ppb health reference level

System ID CA1910033; community water system; California; source: purchased surface water; serves 143,996 people via 33,150 connections; status: active

In focus143,996people served, EPA registry

Public records. Clearer context.

California Water Service Co. - Dominguez is a privately owned community water system in California serving about 143,996 people, matched to 16 ZIP codes.

PFAS and lithium: what EPA's national survey found

EPA tested this water for 30 substances and found 2. Lithium reached 64.7 ppb; EPA's health reference level, which is guidance and not a limit, is 10 ppb.

Between January 2024 and October 2025, EPA's UCMR 5 program tested 570 samples from 9 sampling locations for 30 contaminants (29 PFAS plus lithium). 2 were detected above the reporting level in at least one sample. Lithium reached 64.7 ppb in a single sample, at or above the health reference level of 10 ppb, which is non-regulatory.

Sampling-point average: mean of a location's two (ground water) or four (surface water) UCMR 5 results with non-detects counted as zero, EPA's method for comparing UCMR 5 data to the PFAS MCLs. EPA rounds to the reference value's significant digits before deciding whether an average is "greater than" an MCL (PFOA/PFOS averages count as above 4.0 ng/L only from 4.05 ng/L; lithium results count as above the 10 ppb reference only from 15 ppb). This site does not apply that rounding: "at or above" here means the measured value is numerically at or above the reference.

Utility-reported context (UCMR 5 questionnaire, aggregated across sampling events): PFAS previously found at this system: no at 20 of 20 sampling events; potential PFAS sources nearby: not known at 20 of 20 sampling events.

Lead at customer taps

In the latest completed monitoring period, ending Dec 31, 2023, 9 in 10 sampled homes had lead at or below 1.8 ppb, below the 15 ppb action level that triggers utility action. None of the 25 periods on record reached it.

In the most recent completed lead monitoring period, ending Dec 31, 2023, the 90th-percentile lead result at customer taps was 1.8 ppb, below the action level of 15 ppb (25 monitoring periods on record, none at the action level). The 90th percentile is the value that 9 in 10 sampled homes were at or below. Values are in parts per billion (ppb).

Drinking water violations since Sep 3, 2016

EPA lists 4 violations since Sep 3, 2016. None is health-based. All concern missed monitoring, reporting or public notices, not the water itself.

EPA's SDWIS database lists 4 violations recorded since Sep 3, 2016: 4 for monitoring or reporting, none health-based.

Sanitary surveys and site visits

Most recent state inspection: Oct 30, 2024 (sanitary survey); 1 visit since Sep 3, 2021.

What you can do about these results

ZIP codes served

Sources

Data vintage: EPA UCMR 5 occurrence data, samples collected 2023-01-03 – 2026-06-17, final release, August 2026 (file dated Aug 28, 2026); EPA SDWIS via ECHO, 2026Q2 extract (file dated Jul 9, 2026); EPA service-area boundaries v3.0; Census 2020 ZCTAs. Page generated 2026-09-03.

• EPA ECHO detailed facility report
• EPA UCMR 5 Data Finder
• EPA service-area boundary: modeled, 30.3 sq mi