We read 10 results from Johnston Municipal Water Supply’s 2025 water quality report. No results over a legal limit or above a health goal.
Serves about 24,064 people · Water system ID IA7740011 · 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 |
|---|---|---|---|---|
| Chlorinehighest running annual average · range 0.2 to 1.3 · Johnston distribution · 2025 report, page 6 | 0.8 ppm | None set | 4 ppm | Below the legal limit |
| Copper90th percentile of homes tested · Johnston customer taps · 2025 report, page 6 | 0.03 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)as reported · range 15 to 45 · Johnston distribution · 2025 report, page 6 | 24 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)as reported · range 17 to 55 · Johnston distribution · 2025 report, page 6 | 36 ppb | None set | 80 ppb | Below the legal limit |
| Fluoridehighest measured · range 0.17 to 0.87 · DMWW L.D. McMullen Treatment Plant, highest of 3 sources · 2025 report, page 6 | 0.87 ppm | 1 ppm | 4 ppm | Below the health goal |
| Lead90th percentile of homes tested · Johnston customer taps · 2025 report, page 6 | Not detected | 0.2 ppb | 15 ppb (action level) | Not detected |
| Nitrate (as N)highest measured · range 2.59 to 9.17 · DMWW Fleur Drive Treatment Plant, highest of 3 sources · 2025 report, page 6 | 9.17 ppm | 10 ppm | 10 ppm | Below the health goal |
| Turbidity (cloudiness)highest measured · range 0.02 to 0.25 · DMWW L.D. McMullen Treatment Plant, highest of 3 sources · 2025 report, page 6 | 0.25 NTU | None set | 1 NTU | Below the legal limit |
| Lithiumhighest measured · range 14 to 33 · Johnston distribution · 2025 report, page 6 | 33 ppb | None set | None | No health limit |
| Sodiumhighest measured · range 14.4 to 53.4 · DMWW Fleur Drive Treatment Plant, highest of 3 sources · 2025 report, page 6 | 53.4 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 Johnston Municipal Water Supply’s water between Jan 2025 and Oct 2025. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- Lithium33 ppbFound in 8 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 in this report is above a health goal or legal limit. If you’re bothered by taste, smell, hardness or spots, or your home has older pipes, the filter catalog and buyer questions can help you pick, and a test of your own tap shows what your plumbing adds.
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