Water report · not indexed
What is in the water at 91761
2 public water systems serve this ZIP code in the federal records. Everything below comes from EPA monitoring data, and everything missing is named.
WESTERN MWD
PWSID CA3310049 · CA · serves 86,062 people
PFAS and lithium
4 compounds detected at or above the reporting limit under EPA’s UCMR 5 monitoring, across 5 samples.
| Compound | Highest detected | Samples | Most recent |
|---|---|---|---|
| lithium | 16 µg/L | 1 | 9/14/2023 |
| PFPeA | 0.0047 µg/L | 2 | 4/18/2023 |
| PFHxS | 0.0034 µg/L | 1 | 9/14/2023 |
| PFBS | 0.003 µg/L | 1 | 9/14/2023 |
A detection is a measurement, not a violation and not a health finding. EPA states that UCMR 5 results do not indicate compliance or non-compliance with any limit.
Health-based violations
No open health-based violation on record. This covers MCL, treatment technique and MRDL violations in SDWIS that have not been returned to compliance. It excludes monitoring and reporting violations, which are the large majority nationally, so this is not “no violations”, and SDWIS completeness varies by state.
Hardness
Too few readings to state a hardness. 1 station(s), 1 result(s). Below two stations and five results this page will not state a number: a median of two readings from one creek is not your water.
ONTARIO MUNICIPAL UTILITIES COMPANY
PWSID CA3610034 · CA · serves 185,010 people
PFAS and lithium
6 compounds detected at or above the reporting limit under EPA’s UCMR 5 monitoring, across 8 samples.
| Compound | Highest detected | Samples | Most recent |
|---|---|---|---|
| PFOA | 0.03 µg/L | 1 | 2/28/2023 |
| PFHxA | 0.0071 µg/L | 1 | 2/15/2023 |
| PFPeA | 0.0067 µg/L | 2 | 8/9/2023 |
| PFBA | 0.0064 µg/L | 2 | 2/9/2023 |
| PFOS | 0.0052 µg/L | 1 | 2/15/2023 |
| PFHxS | 0.0042 µg/L | 1 | 2/15/2023 |
A detection is a measurement, not a violation and not a health finding. EPA states that UCMR 5 results do not indicate compliance or non-compliance with any limit.
Health-based violations
No open health-based violation on record. This covers MCL, treatment technique and MRDL violations in SDWIS that have not been returned to compliance. It excludes monitoring and reporting violations, which are the large majority nationally, so this is not “no violations”, and SDWIS completeness varies by state.
Hardness
Too few readings to state a hardness. 2 station(s), 2 result(s). Below two stations and five results this page will not state a number: a median of two readings from one creek is not your water.
What this report cannot tell you
Every figure describes water at a sampling point: a treatment plant, an entry point to the distribution system, or a monitoring station. None of it describes water arriving at your tap. Plumbing between the two can add lead and copper, and if your home was built before 1986 a test kit tells you something no federal dataset can.
Sources: EPA UCMR 5 occurrence (final release, frozen July 2026) · EPA SDWIS health-based violations · USGS and state monitoring via the Water Quality Portal · EPA Public Water System Service Area Boundaries v3. Compiled 2026-09-01.