We read 24 results from Atascadero Mutual Water Co’s 2025 water quality report. No results over a legal limit; 7 above a health goal or guideline.
Serves about 30,618 people · Water system ID CA4010002 · 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 |
|---|---|---|---|---|
| Arsenicaverage · range ND to 2 · listed as a violation in the report · Wells · 2025 report, page 2 | 0.4 ppb | 0.004 ppb | 10 ppb | Above the health goal100x the health goal |
| Copper90th percentile of 60 homes tested, 4 over the action level · listed as a violation in the report · Customer taps · 2025 report, page 2 | 0.95 ppm | 0.3 ppm | 1.3 ppm (action level) | Above the health goal3.2x the health goal |
| Gross alpha (radioactivity)average · range ND to 5.7 · listed as a violation in the report · Wells · 2025 report, page 2 | 2.3 pCi/L | 0 pCi/L | 15 pCi/L | Above the health goalThe health goal is zero |
| PFOA (a PFAS)average · range ND to 17 · Wells · 2025 report, page 2 | 4.9 ppt | 0.007 ppt | 4 ppt from 2029 | Above the federal limit that takes effect in 20291.2x the 4 ppt federal limit that takes effect in 2029Not a violation yet: EPA's 4 ppt limit is final, but water systems don't have to meet it until 2029. |
| PFOS (a PFAS)average · range ND to 32 · Wells · 2025 report, page 2 | 10.9 ppt | 1 ppt | 4 ppt from 2029 | Above the federal limit that takes effect in 20292.7x the 4 ppt federal limit that takes effect in 2029Not a violation yet: EPA's 4 ppt limit is final, but water systems don't have to meet it until 2029. |
| Total dissolved solidsaverage · range 340 to 810 · listed as a violation in the report · Wells · 2025 report, page 2 | 620 ppm | — | 500 ppm guideline | Above the guideline1.2x the guideline (taste, odor or stains; not a health limit) |
| Uraniumaverage · range ND to 3.87 · listed as a violation in the report · printed as 1.68 pCi/L · sampled 2022 · Wells · 2025 report, page 2 | 2.5 ppb | 0.6 ppb | 30 ppb | Above the health goal4.2x the health goal |
| Bariumaverage · range ND to 0.11 · listed as a violation in the report · Wells · 2025 report, page 2 | 0.01 ppm | 2 ppm | 2 ppm | Below the health goal |
| Chlorideaverage · range 23 to 170 · listed as a violation in the report · Wells · 2025 report, page 2 | 99 ppm | — | 250 ppm guideline | Within the guideline |
| Chlorineaverage · range 0.81 to 0.95 · listed as a violation in the report · Distribution system · 2025 report, page 2 | 0.89 ppm | None set | 4 ppm | Below the legal limit |
| Disinfection byproducts (HAA5)as reported · range 7.5 to 16.4 · listed as a violation in the report · Distribution system · 2025 report, page 2 | 14.2 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)as reported · range 36 to 67.9 · listed as a violation in the report · Distribution system · 2025 report, page 2 | 59.2 ppb | None set | 80 ppb | Below the legal limit |
| Fluorideaverage · range ND to 0.43 · listed as a violation in the report · Wells · 2025 report, page 2 | 0.19 ppm | 1 ppm | 2 ppm | Below the health goal |
| Lead90th percentile of 60 homes tested, 0 over the action level · listed as a violation in the report · Customer taps · 2025 report, page 2 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
| Manganeseaverage · range ND to 0.02 · listed as a violation in the report · printed as 4 ppb · Wells · 2025 report, page 2 | 0.004 ppm | — | 0.05 ppm guideline | Within the guideline |
| Nitrate (as N)average · range 0.62 to 5.2 · listed as a violation in the report · Wells · 2025 report, page 2 | 1.87 ppm | 10 ppm | 10 ppm | Below the health goal |
| PFHxS (a PFAS)average · range ND to 19 · Wells · 2025 report, page 2 | 6.4 ppt | None set | 10 ppt from 2029 | Below the legal limit |
| PFNA (a PFAS)average · range ND to 6.6 · Wells · 2025 report, page 2 | 1.2 ppt | None set | 10 ppt from 2029 | Below the legal limit |
| Seleniumaverage · range ND to 7.8 · listed as a violation in the report · Wells · 2025 report, page 2 | 6.2 ppb | 30 ppb | 50 ppb | Below the health goal |
| Sulfateaverage · range 77 to 140 · listed as a violation in the report · Wells · 2025 report, page 2 | 111 ppm | — | 250 ppm guideline | Within the guideline |
| PFBA (a PFAS)average · range ND to 22 · Wells · 2025 report, page 2 | 6.43 ppt | None set | None | No health limit |
| PFBS (a PFAS)average · range ND to 18 · Wells · 2025 report, page 2 | 6.44 ppt | None set | None | No health limit |
| PFHxA (a PFAS)average · range ND to 9.7 · Wells · 2025 report, page 2 | 1.7 ppt | None set | None | No health limit |
| Sodiumaverage · range 26 to 110 · Wells · 2025 report, page 2 | 60 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 Atascadero Mutual Water Co’s water between Apr 2023 and Oct 2023. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- PFOA8.4 pptFound in 2 of 8 samples · highest resultAbove the federal limit that takes effect in 2029 (4 ppt)
- PFOS22.3 pptFound in 4 of 8 samples · highest resultAbove the federal limit that takes effect in 2029 (4 ppt)
- PFHxS7.6 pptFound in 6 of 8 samples · highest resultNo federal limit in force for this one
- PFBS9.4 pptFound in 4 of 8 samples · highest resultNo federal limit in force for this one
- Lithium20.7 ppbFound in 6 of 8 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.
Radium and uranium
Found: Gross alpha (radioactivity), Uranium
What removes it: Reverse osmosis.
PFAS ("forever chemicals")
Found: PFOA (a PFAS), PFOS (a PFAS), PFOA (EPA testing), PFOS (EPA testing)
What removes it: Reverse osmosis.
Salty taste / high TDS
Found: Total dissolved solids
What removes it: Reverse osmosis.
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