We read 12 results from Diablo Water District’s 2025 water quality report. No results over a legal limit; 1 above a health goal or guideline.
Serves about 43,357 people · Water system ID CA0710007 · 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 |
|---|---|---|---|---|
| Lead90th percentile of 32 homes tested, 0 over the action level · Customer taps · 2025 report, page 6 | 1.6 ppb | 0.2 ppb | 15 ppb (action level) | Above the health goal8x the health goal |
| Chloraminehighest running annual average · range ND to 3.3 · Distribution system · 2025 report, page 6 | 2.7 ppm | None set | 4 ppm | Below the legal limit |
| Chlorideaverage · range 46 to 97 · Diablo Water District · 2025 report, page 7 | 67 ppm | — | 250 ppm guideline | Within the guideline |
| Copper90th percentile of 32 homes tested, 0 over the action level · Customer taps · 2025 report, page 6 | 0.12 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)highest running annual average · range 3.1 to 13 · Distribution system · 2025 report, page 6 | 9 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)highest running annual average · range 15 to 21 · Distribution system · 2025 report, page 6 | 24 ppb | None set | 80 ppb | Below the legal limit |
| Nitrate (as N)average · range ND to 0.7 · Diablo Water District · 2025 report, page 6 | 0.5 ppm | 10 ppm | 10 ppm | Below the health goal |
| Sulfateaverage · range 51 to 87 · Diablo Water District · 2025 report, page 7 | 71 ppm | — | 250 ppm guideline | Within the guideline |
| Total dissolved solidsaverage · range 256 to 356 · Diablo Water District · 2025 report, page 7 | 294 ppm | — | 500 ppm guideline | Within the guideline |
| Hardnessaverage · range 5.09 to 8.77 · Diablo Water District · 2025 report, page 7 | 7.25 gpg (124 ppm) | — | — | Hard |
| Lithiumaverage · range ND to 15 · Diablo Water District · 2025 report, page 7 | 10 ppb | None set | None | No health limit |
| Sodiumaverage · range 48 to 77 · Diablo Water District · 2025 report, page 7 | 59 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 Diablo Water District’s water between Mar 2023 and Dec 2023. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- Lithium15 ppbFound in 3 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.
Lead
Found: Lead
What removes it: Certified carbon block or RO.
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