We read 14 results from San Luis Obispo Water Department’s 2025 water quality report. No results over a legal limit; 1 above a health goal or guideline.
Serves about 47,788 people · Water system ID CA4010009 · 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 |
|---|---|---|---|---|
| Gross alpha (radioactivity)as reported · listed as a violation in the report · Treatment plant · 2025 report, page 4 | 1.28 pCi/L | 0 pCi/L | 15 pCi/L | Above the health goalThe health goal is zero |
| Aluminumaverage · range 0.05 to 0.15 · listed as a violation in the report · Treatment plant · 2025 report, page 4 | 0.09 ppm | — | 0.2 ppm guideline | Within the guideline |
| Chlorideas reported · Treatment plant · 2025 report, page 4 | 18 ppm | — | 250 ppm guideline | Within the guideline |
| Chlorineaverage · range 0.14 to 1.8 · listed as a violation in the report · Distribution system · 2025 report, page 4 | 1 ppm | None set | 4 ppm | Below the legal limit |
| Copper90th percentile of 30 homes tested, 0 over the action level · listed as a violation in the report · Customer taps · 2025 report, page 4 | 0.09 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)highest running annual average · range 19 to 68 · listed as a violation in the report · Distribution system · 2025 report, page 4 | 35.9 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)highest running annual average · range 21 to 79 · listed as a violation in the report · Distribution system · 2025 report, page 4 | 45.9 ppb | None set | 80 ppb | Below the legal limit |
| Fluorideaverage · range 0.5 to 1.1 · listed as a violation in the report · Treatment plant · 2025 report, page 4 | 0.71 ppm | 1 ppm | 2 ppm | Below the health goal |
| Lead90th percentile of 30 homes tested, 0 over the action level · listed as a violation in the report · Customer taps · 2025 report, page 4 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
| Sulfateas reported · Treatment plant · 2025 report, page 4 | 74.2 ppm | — | 250 ppm guideline | Within the guideline |
| Turbidity (cloudiness)highest measured · listed as a violation in the report · Treatment plant · 2025 report, page 4 | 0.12 NTU | None set | 1 NTU | Below the legal limit |
| Conductivityas reported · Treatment plant · 2025 report, page 4 | 489 µS/cm | None set | None | No health limit |
| Hardnessaverage · range 8.65 to 17.2 · Treatment plant · 2025 report, page 4 | 12.9 gpg (220 ppm) | — | — | Very hard |
| Sodiumas reported · Treatment plant · 2025 report, page 4 | 23 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 San Luis Obispo Water Department’s water between Jun 2023 and Mar 2024. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- Lithium10 ppbFound in 1 of 4 samples · highest resultBelow EPA’s health reference level of 10 ppb
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.
Radium and uranium
Found: Gross alpha (radioactivity)
What removes it: Reverse osmosis.
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