We read 6 results from Gswc-San Dimas’s 2025 water quality report. No results over a legal limit; 1 above a health goal or guideline.
Serves about 56,538 people · Water system ID CA1910142 · 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 |
|---|---|---|---|---|
| Bromatehighest running annual average · range ND to 12 · Distribution system · 2025 report, page 9 | 3 ppb | 0.1 ppb | 10 ppb | Above the health goal30x the health goal |
| Chlorineaverage · range 0.2 to 3.6 · Distribution system · 2025 report, page 9 | 1.9 ppm | None set | 4 ppm | Below the legal limit |
| Copper90th percentile of 31 homes tested, 0 over the action level · sampled 2023 · Customer taps · 2025 report, page 9 | 0.29 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)average · range 1.7 to 26 · Distribution system · 2025 report, page 9 | 14 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)highest running annual average · range ND to 92 · Distribution system · 2025 report, page 9 | 45 ppb | None set | 80 ppb | Below the legal limit |
| Lead90th percentile of 31 homes tested, 0 over the action level · sampled 2023 · Customer taps · 2025 report, page 9 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
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 Gswc-San Dimas’s water between Nov 2024 and Aug 2025. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- PFOS4.6 pptFound in 2 of 20 samples · highest resultAbove the federal limit that takes effect in 2029 (4 ppt)
- Lithium57 ppbFound in 4 of 20 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.
PFAS ("forever chemicals")
Found: PFOS (EPA testing)
What removes it: Reverse osmosis.
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