We read 13 results from Rincon del Diablo MWD (ID-1)’s 2025 water quality report. No results over a legal limit; 2 above a health goal or guideline.
Serves about 30,757 people · Water system ID CA3710018 · 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 30 homes tested, 0 over the action level · Customer taps · 2025 report, page 11 | 0.41 ppm | 0.3 ppm | 1.3 ppm (action level) | Above the health goal1.4x the health goal |
| Total dissolved solidsaverage · range 424 to 635 · Lake Skinner plant · 2025 report, page 17 | 525 ppm | — | 500 ppm guideline | Above the guideline1.1x the guideline (taste, odor or stains; not a health limit) |
| Chloramineaverage · range 1.32 to 1.85 · Distribution system · 2025 report, page 9 | 1.67 ppm | None set | 4 ppm | Below the legal limit |
| Chlorideaverage · range 87 to 91 · Lake Skinner plant · 2025 report, page 17 | 89 ppm | — | 250 ppm guideline | Within the guideline |
| Disinfection byproducts (HAA5)highest running annual average · range ND to 12 · Distribution system · 2025 report, page 9 | 5 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)highest running annual average · range 16 to 32 · Distribution system · 2025 report, page 9 | 22 ppb | None set | 80 ppb | Below the legal limit |
| Fluorideaverage · range 0.6 to 0.8 · Lake Skinner plant · 2025 report, page 17 | 0.7 ppm | 1 ppm | 2 ppm | Below the health goal |
| Lead90th percentile of 30 homes tested, 1 over the action level · Customer taps · 2025 report, page 11 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
| Sulfateaverage · range 164 to 171 · Lake Skinner plant · 2025 report, page 17 | 168 ppm | — | 250 ppm guideline | Within the guideline |
| Turbidity (cloudiness)highest measured · Lake Skinner plant · 2025 report, page 17 | 0.07 NTU | None set | 1 NTU | Below the legal limit |
| Hardnessaverage · range 13.3 to 13.6 · Lake Skinner plant · 2025 report, page 17 | 13.5 gpg (230 ppm) | — | — | Very hard |
| Lithiumhighest measured · Entry point (UCMR 5) · 2025 report, page 15 | 43 ppb | None set | None | No health limit |
| Sodiumaverage · range 83 to 87 · Lake Skinner plant · 2025 report, page 17 | 85 ppm | 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 Rincon del Diablo MWD (ID-1)’s water between Mar 2025 and Feb 2026. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- Lithium43 ppbFound in 4 of 4 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.
Salty taste / high TDS
Found: Total dissolved solids
What removes it: Reverse osmosis.
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