We read 17 results from Contra Costa Water District’s 2025 water quality report. No results over a legal limit; 1 above a health goal or guideline.
Serves about 198,000 people · Water system ID CA0710003 · Read the district’s 2025 report (opens in a new tab)
Open this district in the water lookupCompare with your own test results, see the district map and get matched filters.
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 |
|---|---|---|---|---|
| Total coliform bacteriahighest month · range ND to 0.6 · Distribution system · 2025 report, page 6 | 0.6 % positive | 0 % positive | 5 % positive | Above the health goalThe health goal is zero |
| Chloraminesystem-wide average · range ND to 3.4 · Distribution system · 2025 report, page 6 | 2.1 ppm | None set | 4 ppm | Below the legal limit |
| Chlorideaverage · range 22 to 101 · Randall-Bold plant · 2025 report, page 7 | 46 ppm | — | 250 ppm guideline | Within the guideline |
| Chromium-6highest measured · Treatment plants · 2025 report, page 6 | 0.02 ppb | 0.02 ppb | 10 ppb | Below the health goal |
| Copper90th percentile of 64 homes tested, 0 over the action level · Customer taps (64 sites) · 2025 report, page 6 | 0.11 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)system-wide average · range 4.4 to 21 · Distribution system · 2025 report, page 6 | 16 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)system-wide average · range 13 to 33 · Distribution system · 2025 report, page 6 | 28 ppb | None set | 80 ppb | Below the legal limit |
| Fluorideaverage · range 0.6 to 0.8 · Treatment plants · 2025 report, page 5 | 0.7 ppm | 1 ppm | 2 ppm | Below the health goal |
| Lead90th percentile of 64 homes tested, 1 over the action level · Customer taps (64 sites) · 2025 report, page 6 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
| pHaverage · range 8.1 to 8.7 · Bollman plant · 2025 report, page 7 | 8.5 | — | — | Normal range |
| Sulfateaverage · range 46 to 66 · Bollman plant · 2025 report, page 7 | 58 ppm | — | 250 ppm guideline | Within the guideline |
| Total dissolved solidsaverage · range 159 to 281 · Bollman plant · 2025 report, page 7 | 212 ppm | — | 500 ppm guideline | Within the guideline |
| Turbidity (cloudiness)highest measured · Randall-Bold plant, highest of 2 sources · 2025 report, page 6 | 0.8 NTU | None set | 1 NTU | Below the legal limit |
| Alkalinityaverage · range 48 to 63 · Bollman plant · 2025 report, page 7 | 55 ppm | None set | None | No health limit |
| Calciumaverage · range 12 to 17 · Bollman plant · 2025 report, page 7 | 15 ppm | None set | None | No health limit |
| Hardnessaverage · range 3.45 to 5.26 · Bollman plant · 2025 report, page 7 | 4.33 gpg (74 ppm) | — | — | Moderately hard |
| Sodiumaverage · range 35 to 68 · Bollman plant · 2025 report, page 7 | 47 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.
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.
Bacteria and viruses
Found: Total coliform bacteria
What removes it: UV purification (and tell your utility).
More districts: California water quality · All states · Something look wrong? Tell us