We read 19 results from Ofallon Pws’s 2025 water quality report. No results over a legal limit; 2 above a health goal or guideline.
Serves about 32,515 people · Water system ID MO6010588 · 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 homes tested, 0 over the action level · Customer taps · 2025 report, page 2 | 1.48 ppb | 0.2 ppb | 15 ppb (action level) | Above the health goal7.4x the health goal |
| Total dissolved solidshighest measured · range 241 to 658 · sampled 2023 · 2025 report, page 4 | 658 ppm | — | 500 ppm guideline | Above the guideline1.3x the guideline (taste, odor or stains; not a health limit) |
| Chloridehighest measured · range 25.4 to 173 · sampled 2023 · 2025 report, page 4 | 173 ppm | — | 250 ppm guideline | Within the guideline |
| Copper90th percentile of homes tested, 0 over the action level · Customer taps · 2025 report, page 2 | 0.1 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)highest running annual average · range 4 to 31.3 · Purchased water: Distribution system, highest of 5 sources · 2025 report, page 3 | 29 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)highest running annual average · range 1.6 to 50.2 · Purchased water: Distribution system, highest of 5 sources · 2025 report, page 3 | 47 ppb | None set | 80 ppb | Below the legal limit |
| Ironhighest measured · range ND to 0.05 · sampled 2023 · 2025 report, page 4 | 0.05 ppm | — | 0.3 ppm guideline | Within the guideline |
| Manganesehighest measured · range ND to 0.0018 · sampled 2023 · 2025 report, page 4 | 0.0018 ppm | — | 0.05 ppm guideline | Within the guideline |
| pHhighest measured · range 7.91 to 8.08 · sampled 2023 · 2025 report, page 4 | 8.08 | — | — | Normal range |
| Sulfatehighest measured · range 20.8 to 65 · sampled 2023 · 2025 report, page 4 | 65 ppm | — | 250 ppm guideline | Within the guideline |
| Zinchighest measured · range 0.0026 to 0.05 · sampled 2023 · 2025 report, page 4 | 0.05 ppm | — | 5 ppm guideline | Within the guideline |
| Alkalinityhighest measured · range 150 to 302 · sampled 2023 · 2025 report, page 4 | 302 ppm | None set | None | No health limit |
| Calciumhighest measured · range 32.1 to 62.4 · sampled 2023 · 2025 report, page 4 | 62.4 ppm | None set | None | No health limit |
| Hardnesshighest measured · range 7.19 to 16.6 · sampled 2023 · 2025 report, page 4 | 16.6 gpg (283 ppm) | — | — | Very hard |
| Lithiumhighest measured · range 28.1 to 28.1 · 2025 report, page 4 | 28.1 ppb | None set | None | No health limit |
| Magnesiumhighest measured · range 9.21 to 30.8 · sampled 2023 · 2025 report, page 4 | 30.8 ppm | None set | None | No health limit |
| Nickelhighest measured · range ND to 1.39 · printed as 0.00139 MG/L · sampled 2023 · 2025 report, page 4 | 1.39 ppb | None set | None | No health limit |
| Potassiumhighest measured · range 1.31 to 7.78 · sampled 2023 · 2025 report, page 4 | 7.78 ppm | None set | None | No health limit |
| Sodiumhighest measured · range 33.6 to 182 · sampled 2023 · 2025 report, page 4 | 182 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. 35 numbers we weren’t sure about are held back until a person checks.
EPA testing for PFAS and lithium
EPA’s own nationwide testing (UCMR 5) found these in Ofallon Pws’s water between Feb 2024 and Sep 2025. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- Lithium71.3 ppbFound in 10 of 12 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.
Salty taste / high TDS
Found: Total dissolved solids
What removes it: Reverse osmosis.
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