No health-based violations on EPA record since 2016.
Serves about 102,348 people (25,440 connections) with surface water bought from San Francisco Regional Water System.
From EPA's record for CA4110008. PurityMap is independent of California Water Service.
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No health-based violations in the last 10 years, from EPA's SDWIS compliance database.
EPA required this system to test for 30 unregulated and emerging contaminants, from May 2024 to February 2025.
| Contaminant | Result | Limit | Status | Sampled | Source |
|---|---|---|---|---|---|
| 11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (11Cl-PF3OUdS) | < 5 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| 1H, 1H, 2H, 2H-perfluorodecane sulfonic acid (8:2 FTS) | < 5 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| 1H, 1H, 2H, 2H-perfluorohexane sulfonic acid (4:2 FTS) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| 1H, 1H, 2H, 2H-perfluorooctane sulfonic acid (6:2 FTS) | < 5 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| 4,8-Dioxa-3H-perfluorononanoic acid (ADONA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| 9-Chlorohexadecafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS) | < 2 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Hexafluoropropylene oxide dimer acid (HFPO-DA) (GenX chemicals) | < 5 ng/L | 10 ng/L federal MCL (2024) | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Lithium | < 9 µg/L | 10 µg/L EPA health reference level (screening, not a legal limit)Screening level, not a legal limit | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA) | < 5 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA) | < 6 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Nonafluoro-3,6-dioxaheptanoic acid (NFDHA) | < 20 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoro (2-ethoxyethane) sulfonic acid (PFEESA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoro-3-methoxypropanoic acid (PFMPA) | < 4 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoro-4-methoxybutanoic acid (PFMBA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorobutanesulfonic acid (PFBS) | < 3 ng/L | 2,000 ng/L EPA health advisory (screening, not a legal limit)Screening level, not a legal limit | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorobutanoic acid (PFBA) | < 5 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorodecanoic acid (PFDA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorododecanoic acid (PFDoA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoroheptanesulfonic acid (PFHpS) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoroheptanoic acid (PFHpA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorohexanesulfonic acid (PFHxS) | < 3 ng/L | 10 ng/L federal MCL (2024) | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorohexanoic acid (PFHxA) | < 3 ng/L | 400,000 ng/L Michigan EGLE state MCL (strictest US state) | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorononanoic acid (PFNA) | < 4 ng/L | 10 ng/L federal MCL (2024) | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorooctanesulfonic acid (PFOS) | < 4 ng/L | 4.0 ng/L federal MCL (2024) | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorooctanoic acid (PFOA) | < 4 ng/L | 4.0 ng/L federal MCL (2024) | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoropentanesulfonic acid (PFPeS) | < 4 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoropentanoic acid (PFPeA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorotetradecanoic acid (PFTA) | < 8 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluorotridecanoic acid (PFTrDA) | < 7 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
| Perfluoroundecanoic acid (PFUnA) | < 2 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2024-05-16 to 2025-02-03 | UCMR5 Analytical Results: CALIFORNIA WATER SERVICE - SAN MATEO (CA4110008) |
Screening tells you if something is worth a closer look; a lab result is the number you can act on.
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Screening: quick check, not lab-grade
Safe Home (EnviroTestKits)
Lead, read as one of three ranges: 0–4, 5–15 or 15+ ppb
Turnaround: 5 minutes
What it can't tell you: It shows a lead range, not an exact level, and tests nothing else unless you pay extra for the optional lab test.
Lab-certified results
ETR Laboratories
50+ substances, including lead, copper, arsenic, nitrate, hardness and coliform bacteria
Environmental Testing and Research Laboratories (ETR Labs), Leominster, MA · ISO/IEC 17025:2017, ANAB certificate AT-2638 · 2–4 business days after the lab receives it
What it can't tell you: It does not test PFAS, and not every result on the panel falls under the lab's accredited scope.
Get PurityMap updates about this water system.
Follow this water →California Water Service's phone number on EPA record is 408-367-8593. Its mailing address is 1720 NORTH FIRST STREET, SAN JOSE, CA 95112.
According to EPA's record, California Water Service uses surface water bought from San Francisco Regional Water System.
No health-based violations on EPA record since 2016. The record comes from EPA's SDWIS compliance database.
The 90th-percentile lead result in California Water Service's latest lead and copper round, which ended in December 2025, was 4.4 µg/L, below the federal action level of 15 µg/L.
PurityMap has no verified website for California Water Service. Its phone number on EPA record is 408-367-8593. Its mailing address on EPA record is 1720 NORTH FIRST STREET, SAN JOSE, CA 95112. Your water bill lists the ways to contact your supplier and pay. PurityMap does not take payments.