We read 16 results from Great Oaks Wc INC’s 2025 water quality report. No results over a legal limit; 3 above a health goal or guideline.
Serves about 110,088 people · Water system ID CA4310022 · Read the district’s 2025 report (opens in a new tab)
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Results from the 2025 report
Each number is copied from the district’s report and links to the page it’s printed on. Where the report lists several plants, wells or purchased water, the highest is shown.
| Contaminant | Result | Health goal | Legal limit | What it means |
|---|---|---|---|---|
| Copper90th percentile of 57 homes tested, 0 over the action level · sampled 2023 · Customer taps · 2025 report, page 2 | 0.38 ppm | 0.3 ppm | 1.3 ppm (action level) | Above the health goal1.3x the health goal |
| Gross alpha (radioactivity)average · range ND to 2.62 · Wells · 2025 report, page 2 | 0.7 pCi/L | 0 pCi/L | 15 pCi/L | Above the health goalThe health goal is zero |
| Radium (combined 226 + 228)average · range ND to 0.79 · Wells · 2025 report, page 2 | 0.13 pCi/L | 0 pCi/L | 5 pCi/L | Above the health goalThe health goal is zero |
| Bariumaverage · range ND to 0.15 · Wells · 2025 report, page 2 | 0.03 ppm | 2 ppm | 2 ppm | Below the health goal |
| Chlorideaverage · range 36 to 55 · Wells · 2025 report, page 2 | 40 ppm | — | 250 ppm guideline | Within the guideline |
| Chlorinehighest running annual average · Distribution system · 2025 report, page 2 | 0.23 ppm | None set | 4 ppm | Below the legal limit |
| Disinfection byproducts (HAA5)as reported · Calero Pressure Zone · 2025 report, page 2 | 2.9 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)as reported · Calero Pressure Zone · 2025 report, page 2 | 23.5 ppb | None set | 80 ppb | Below the legal limit |
| Fluorideaverage · range 0.11 to 0.21 · Wells · 2025 report, page 2 | 0.14 ppm | 1 ppm | 2 ppm | Below the health goal |
| Ironaverage · range ND to 0.12 · Wells · 2025 report, page 2 | 0.0027 ppm | — | 0.3 ppm guideline | Within the guideline |
| Lead90th percentile of 57 homes tested, 0 over the action level · printed as ND ppm · sampled 2023 · Customer taps · 2025 report, page 2 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
| Nitrate (as N)average · range 0.71 to 6.5 · Wells · 2025 report, page 2 | 1.34 ppm | 10 ppm | 10 ppm | Below the health goal |
| Sulfateaverage · range 35 to 58 · Wells · 2025 report, page 2 | 40 ppm | — | 250 ppm guideline | Within the guideline |
| Total coliform bacteriahighest month · Distribution system · 2025 report, page 2 | Not detected | 0 % positive | 5 % positive | Not detected |
| Total dissolved solidsaverage · range 270 to 440 · Wells · 2025 report, page 2 | 307 ppm | — | 500 ppm guideline | Within the guideline |
| Conductivityaverage · range 530 to 790 · Wells · 2025 report, page 2 | 584 µS/cm | None set | None | No health limit |
Utility results describe the whole system, measured where water enters the pipes, not your tap. Your home’s plumbing can add lead or copper.
EPA testing for PFAS and lithium
EPA’s own nationwide testing (UCMR 5) found these in Great Oaks Wc INC’s water between Jun 2025 and Dec 2025. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- PFOS4.6 pptFound in 1 of 38 samples · highest resultAbove the federal limit that takes effect in 2029 (4 ppt)
- PFHxS8 pptFound in 5 of 38 samples · highest resultNo federal limit in force for this one
- Lithium16 ppbFound in 34 of 38 samples · highest resultAbove EPA’s health reference level of 10 ppb (a guide, not a legal limit)
Source: EPA UCMR 5 occurrence data. The highest single result is shown; one high sample doesn’t mean every glass is that high.
What you can do
Nothing here is an emergency notice: if the district has a violation, it must tell customers directly. If you’d like to lower these at your tap, these are the treatments that remove them, and the catalog shows the models certified for each. Ranking is by certified removal; commissions never change the order.
Copper
Found: Copper
What removes it: Reverse osmosis.
Radium and uranium
Found: Gross alpha (radioactivity), Radium (combined 226 + 228)
What removes it: Reverse osmosis.
PFAS ("forever chemicals")
Found: PFOS (EPA testing)
What removes it: Reverse osmosis.
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