We read 16 results from Marin Municipal Water District’s 2025 water quality report. No results over a legal limit; 2 above a health goal or guideline.
Serves about 186,895 people · Water system ID CA2110002 · 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 |
|---|---|---|---|---|
| Chromium-6average · range 0.16 to 0.37 · Distribution system · 2025 report, page 8 | 0.25 ppb | 0.02 ppb | 10 ppb | Above the health goal13x the health goal |
| Total coliform bacteriahighest month · Distribution system · 2025 report, page 8 | 0.7 % positive | 0 % positive | 5 % positive | Above the health goalThe health goal is zero |
| Chloramineaverage · range ND to 3.1 · Distribution system · 2025 report, page 8 | 1.82 ppm | None set | 4 ppm | Below the legal limit |
| Chlorideaverage · range 8.8 to 16 · Marin reservoir water · 2025 report, page 9 | 11 ppm | — | 250 ppm guideline | Within the guideline |
| Copper90th percentile of 54 homes tested, 0 over the action level · sampled 2024 · Customer taps (54 sites) · 2025 report, page 8 | 0.16 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)highest running annual average · range 3 to 26 · Distribution system · 2025 report, page 8 | 19 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)highest running annual average · range 11 to 63 · Distribution system · 2025 report, page 8 | 41 ppb | None set | 80 ppb | Below the legal limit |
| Fluorideaverage · range 0.5 to 0.8 · Distribution system · 2025 report, page 9 | 0.7 ppm | 1 ppm | 2 ppm | Below the health goal |
| Lead90th percentile of 54 homes tested, 0 over the action level · sampled 2024 · Customer taps (54 sites) · 2025 report, page 8 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
| Nitrate (as N)average · range ND to 0.43 · Distribution system · 2025 report, page 8 | 0.43 ppm | 10 ppm | 10 ppm | Below the health goal |
| pHaverage · range 7.5 to 9.6 · Distribution system · 2025 report, page 9 | 8 | — | — | Normal range |
| Total dissolved solidsaverage · range 150 to 180 · SCWA water, highest of 2 sources · 2025 report, page 9 | 164 ppm | — | 500 ppm guideline | Within the guideline |
| Turbidity (cloudiness)highest measured · range 0.02 to 0.09 · Treatment plants · 2025 report, page 8 | 0.09 NTU | None set | 1 NTU | Below the legal limit |
| Hardnessaverage · range 6.43 to 7.02 · SCWA water, highest of 2 sources · 2025 report, page 9 | 6.55 gpg (112 ppm) | — | — | Moderately hard |
| Radonaverage · SCWA water · 2025 report, page 9 | 78 pCi/L | None set | None | No health limit |
| Sodiumaverage · range 17 to 27 · Marin reservoir water · 2025 report, page 9 | 22 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).
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