No health-based violations on EPA record since 2016.
Serves about 110,088 people (21,415 connections) with groundwater from its own wells, and buys water from San Jose Water.
From EPA's record for CA4310022. PurityMap is independent of Great Oaks WC Inc.
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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 June 2025 to December 2025.
| Contaminant | Result | Limit | Status | Sampled | Source |
|---|---|---|---|---|---|
| Lithium | 16 µg/L | 10 µg/L EPA health reference level (screening, not a legal limit)Screening level, not a legal limit | Above the referenced health-based guidance value | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorooctanesulfonic acid (PFOS) | 4.6 ng/L | 4.0 ng/L federal MCL (2024) | Above a historical reference; current applicability unverified | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorohexanesulfonic acid (PFHxS) | 8 ng/L | 10 ng/L federal MCL (2024) | Within a historical reference; current applicability unverified | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorohexanoic acid (PFHxA) | 4.5 ng/L | 400,000 ng/L Michigan EGLE state MCL (strictest US state) | Within a historical reference; current applicability unverified | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoropentanoic acid (PFPeA) | 4.7 ng/L | No federal or state limit; shown for transparency | Detected, no limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| 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 | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| 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 | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| 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 | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| 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 | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| 4,8-Dioxa-3H-perfluorononanoic acid (ADONA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| 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 | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Hexafluoropropylene oxide dimer acid (HFPO-DA) (GenX chemicals) | < 5 ng/L | 10 ng/L federal MCL (2024) | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA) | < 5 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA) | < 6 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Nonafluoro-3,6-dioxaheptanoic acid (NFDHA) | < 20 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoro (2-ethoxyethane) sulfonic acid (PFEESA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoro-3-methoxypropanoic acid (PFMPA) | < 4 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoro-4-methoxybutanoic acid (PFMBA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| 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 | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorobutanoic acid (PFBA) | < 5 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorodecanoic acid (PFDA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorododecanoic acid (PFDoA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoroheptanesulfonic acid (PFHpS) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoroheptanoic acid (PFHpA) | < 3 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorononanoic acid (PFNA) | < 4 ng/L | 10 ng/L federal MCL (2024) | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorooctanoic acid (PFOA) | < 4 ng/L | 4.0 ng/L federal MCL (2024) | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoropentanesulfonic acid (PFPeS) | < 4 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorotetradecanoic acid (PFTA) | < 8 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluorotridecanoic acid (PFTrDA) | < 7 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
| Perfluoroundecanoic acid (PFUnA) | < 2 ng/L | No federal or state limit; shown for transparency | Not detected above the reporting limit | 2025-06-24 to 2025-12-17 | UCMR5 Analytical Results: GREAT OAKS WC INC (CA4310022) |
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 →Great Oaks WC Inc's phone number on EPA record is 408-227-9540. Its mailing address is 20 Great Oaks Blvd., Suite 120, SAN JOSE, CA 95119.
According to EPA's record, Great Oaks WC Inc uses groundwater from its own wells, and buys water from San Jose Water.
No health-based violations on EPA record since 2016. The record comes from EPA's SDWIS compliance database.
Lead was not detected at the 90th percentile of tap samples in Great Oaks WC Inc's latest lead and copper round, which ended in December 2023. The federal action level is 15 µg/L.
PurityMap has no verified website for Great Oaks WC Inc. Its phone number on EPA record is 408-227-9540. Its mailing address on EPA record is 20 Great Oaks Blvd., Suite 120, SAN JOSE, CA 95119. Your water bill lists the ways to contact your supplier and pay. PurityMap does not take payments.