Great Oaks Water Company Inc water quality
San Jose, CA · serves 112,582 people (21,578 connections) · Groundwater · Private · EPA ID CA4310022
Data: U.S. EPA · How we read the data · How we check it
Buys water from San Jose Water. Treated water bought from another system can carry that system's contaminants.
Summary
No federal limits exceeded in EPA data.
- PFAS
- Detected, below limit4 of 29 PFAS found at least once. All averages below the federal limits.
- Lithium
- Above screening levelHighest result 16 ppb. EPA uses 10 ppb to decide what to study further. It is not a health limit, and there is no federal limit for lithium. About 1 in 4 systems tested were above it.
- Lead
- Below action level0 ppb (parts per billion) at the 90th percentile: 9 in 10 homes sampled were at or below it. Action level 15 ppb, falling to 10 ppb in Nov 2027. Monitoring period Jan 2024 – now, still in progress (results reported so far). Your home's pipes can make yours higher.
- Violations
- None health-basedNo health-based violations since 2016.
- Built before 1986, or not sure what your service line is made of? Check your service line and test your tap. Utility data can't show your pipes.
- Want to reduce what was found? Filters for these results.
- Tested your own tap? Compare your result with these numbers. Moving? Compare this system with another.
- Read Great Oaks Water Company Inc's annual water quality report (Consumer Confidence Report). It lists every regulated contaminant tested and is usually on the utility's website or mailed with your bill, and you can also request it at (408) 227-9540. EPA: how to find it.
PFAS (“forever chemicals”)
EPA UCMR 5: 19 entry points tested Jun 2025 to Dec 2025. "Average" is the highest entry-point average (non-detects counted as zero), the way EPA compares UCMR 5 results to the limits. ppt = parts per trillion. These results do not determine compliance.
| Contaminant | Highest average |
|---|---|
| PFOA Not detected Limit 4 ppt | – |
| PFOS One sample above limit Limit 4 ppt | 2.3 ppt 57% of the limit |
| PFHxS Detected, below limit Limit 10 ppt | 6.7 ppt 67% of the limit |
| PFNA Not detected Limit 10 ppt | – |
| HFPO-DA (GenX) Not detected Limit 10 ppt | – |
| Hazard Index (a combined score for PFHxS, PFNA, GenX and PFBS, where above 1 is over the limit) Detected, below limit Limit 1 | 0.67 |
| PFBS Not detected Guideline 2,000 ppt | – |
| PFBA Not detected Guideline 6,000 ppt | – |
| PFHxA Detected, below limit Guideline 3,000 ppt | 4.25 ppt |
| PFPeA Detected, no limit | 4.6 ppt |
29 PFAS tested, 4 detected at least once. "Not detected" means below EPA's reporting limit (about 2 to 20 ppt depending on the chemical), not proven zero. PFAS not listed were not detected. The limits for PFHxS, PFNA, GenX and the Hazard Index were proposed for rescission in May 2026. That proposal is not final. Systems have until 2029 to meet the limits.
Lithium
Detected in 34 of 38 samples. Highest result 16 ppb. EPA's non-enforceable screening level is 10 ppb. Above screening level The screening level is how EPA decides what to study further, not a health limit. There is no federal limit for lithium and no filter is certified to remove it. About lithium.
Lead and copper
Latest 90th percentile: 0 ppb lead (Jan 2024 – now (in progress)). Below action level
Highest since 2016: 4.4 ppb (Dec 2017).
| Monitoring period | Lead (90th pct.) |
|---|---|
| Jan 2024 – now (in progress) | 0 ppb |
| Jan 2021 – Dec 2023 | 0 ppb |
| Jan 2018 – Dec 2020 | 1.2 ppb |
Earlier results (9)
| Jan 2015 – Dec 2017 | 4.4 ppb |
| Jan 2012 – Dec 2014 | 4 ppb |
| Jan 2011 – Dec 2013 | 2.9 ppb |
| Jan 2008 – Dec 2010 | 0 ppb |
| Jan 2005 – Dec 2007 | 5 ppb |
| Jan 2006 – Dec 2006 | 16 ppb |
| Jan 2004 – Dec 2006 | 6.5 ppb |
| Jan 2005 – Dec 2005 | 5 ppb |
| Jan 2004 – Dec 2004 | 6.5 ppb |
Lead comes from pipes and fixtures, not the source water, so it varies home to home. The 90th percentile means 9 in 10 sampled homes were at or below it. More on lead.
Violations
Health-based violations mean a contaminant exceeded a limit or a required treatment step was missed. Monitoring and reporting violations mean required tests or reports were late or missing, so the water's quality during that time is unknown. The total includes every violation in EPA's records, most of them paperwork.
Earlier EPA testing (2013–2020)
| Contaminant | Highest | Guideline |
|---|---|---|
| Manganese | 2.3 ppb | 300 ppb |
| Chromium-6 | 6.8 ppb | – |
| Vanadium | 2.8 ppb | 21 ppb |
| Chlorate | 60 ppb | 210 ppb |
| Molybdenum | 1.1 ppb | 40 ppb |
| Strontium | 0.85 ppm | 1.5 ppm |
Where it serves
ZIP codes the system reported serving: 95037, 95111, 95119, 95120, 95123, 95136, 95138, 95139, 95193
Nearby utilities
- City of San Jose – Evergreen/Edenvale/Coyote San Jose · same area
- San Jose Water San Jose · same area
- City of Santa Clara Santa Clara · 10 mi
- City of Milpitas Milpitas · 10 mi
- City of Sunnyvale Sunnyvale · 13 mi
- Alameda County Water District Fremont · 15 mi
Questions
Is Great Oaks Water Company Inc water safe to drink?
Great Oaks Water Company Inc has no health-based violations since 2016. EPA testing found no PFAS above the federal limits. Federal data can't tell you about your own pipes: lead comes from service lines and plumbing, so test your tap if your home was built before 1986. For the official word, read the utility's annual Consumer Confidence Report.
Does Great Oaks Water Company Inc water have PFAS?
Yes. EPA's 2023–2025 testing of Great Oaks Water Company Inc found 4 PFAS at least once. None of the averages were above the federal limits.
What is the lead level in Great Oaks Water Company Inc water?
The most recent 90th-percentile lead result for Great Oaks Water Company Inc is 0 ppb, for the monitoring period that began Jan 2024 (still in progress). The federal action level is 15 ppb, falling to 10 ppb in November 2027. The 90th percentile means 9 in 10 homes sampled were at or below this number. Individual homes can be higher.
Check these numbers yourself
Every figure on this page comes from public EPA records. You don't have to take our word for it:
- EPA's own report for CA4310022: violations, enforcement and inspections, straight from EPA.
- EPA UCMR 5 data: the PFAS and lithium results (search the file for PWSID CA4310022).
- EPA SDWIS download: the lead results, population and violation records we use.
- The utility's annual water quality report (Consumer Confidence Report): ask Great Oaks Water Company Inc at (408) 227-9540, or see EPA's guide to finding it.
Found something that doesn't match? Tell us and we'll check it against EPA's records. How we check our data.
Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.