What was found in O'Fallon's water
The level at the city's main supplier, the highest level anywhere in the city, the EPA limit for each, and where every figure comes from.
| Contaminant | Level vs EPA limit | Suppliers | Source |
|---|---|---|---|
| Fluoride | 632 µg/L 16% of the EPA limit 4000 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2017
Highest in the city: 1833 µg/L — ST PAUL PWS · 1,700 people · 2018 | 5/5 | SYR4 |
| Nitrate-Nitrite | 1442.5 µg/L 14% of the EPA limit 10000 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019 | 5/5 | SYR4 |
| Copper | 64.215 µg/L 4.9% of the EPA limit 1300 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 224 µg/L — ST CHARLES CO PWSD 2 - SUMAC RIDGE · 103 people · 2018 | 5/5 | SYR4 |
| Barium | 142.4 µg/L 7.1% of the EPA limit 2000 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2017 | 5/5 | SYR4 |
| TTHM | 37.695 µg/L 47% of the EPA limit 80 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 76.62 µg/L — ST PAUL PWS · 1,700 people · 2018 | 5/5 | SYR4 |
| Lithium | 47.5 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2025
Highest in the city: 71.3 µg/L — OFALLON PWS · 32,515 people · 2025 | 2/5 | UCMR-5 |
| Total Haloacetic Acids (HAA5) | 32.56 µg/L 54% of the EPA limit 60 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019 | 4/5 | SYR4 |
| Chloroform | 25.45 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 32.245 µg/L — ST PAUL PWS · 1,700 people · 2018 | 5/5 | SYR4 |
| Dichloroacetic Acid | 29.02 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019 | 5/5 | SYR4 |
| Bromodichloromethane | 8.97 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 19.805 µg/L — ST PAUL PWS · 1,700 people · 2018 | 5/5 | SYR4 |
| Dibromochloromethane | 4.556 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 19.425 µg/L — ST PAUL PWS · 1,700 people · 2018 | 5/5 | SYR4 |
| Monobromoacetic Acid | 8.9625 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 12.075 µg/L — ST PAUL PWS · 1,700 people · 2018 | 4/5 | SYR4 |
| Gross Alpha, Excl. Radon And U | 12.05 pCi/L 80% of the EPA limit 15 pCi/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2015 | 1/5 | SYR4 |
| Selenium | 11 µg/L 22% of the EPA limit 50 µg/L Highest in the city: OFALLON PWS · 32,515 people · 2017 | 1/5 | SYR4 |
| Monochloroacetic Acid | 9.7 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019 | 1/5 | SYR4 |
| Lead | 3.45 µg/L 23% of the EPA limit 15 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 8.555 µg/L — ST CHARLES CO PWSD 2 AUGUSTA · 881 people · 2019 | 5/5 | SYR4 |
| Bromoform | 0.7285 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 8.1465 µg/L — ST PAUL PWS · 1,700 people · 2018 | 3/5 | SYR4 |
| Chromium | 2.404 µg/L 2.4% of the EPA limit 100 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2017
Highest in the city: 7.444 µg/L — OFALLON PWS · 32,515 people · 2017 | 4/5 | SYR4 |
| Trichloroacetic Acid | 5.1875 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019 | 5/5 | SYR4 |
| Combined Radium (-226 And -228) | 3.245 pCi/L 65% of the EPA limit 5 pCi/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 5.14 pCi/L — OFALLON PWS · 32,515 people · 2019 | 4/5 | SYR4 |
| Dibromoacetic Acid | 1.871 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2019
Highest in the city: 3.714 µg/L — ST PAUL PWS · 1,700 people · 2018 | 4/5 | SYR4 |
| Xylenes, Total | 2.764 µg/L 0% of the EPA limit 10000 µg/L Highest in the city: ST CHARLES CO PWSD 2 AUGUSTA · 881 people · 2017 | 2/5 | SYR4 |
| Arsenic | 2.269 µg/L 23% of the EPA limit 10 µg/L Highest in the city: OFALLON PWS · 32,515 people · 2017 | 1/5 | SYR4 |
| Atrazine | 0.3300 µg/L 11% of the EPA limit 3 µg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2016 | 1/5 | SYR4 |
| Pfba | 0.0065 µg/L No EPA limit set Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2025 | 2/5 | UCMR-5 |
| Pfpea | 0.0034 µg/L No EPA limit set Highest in the city: OFALLON PWS · 32,515 people · 2025 | 1/5 | UCMR-5 |
| Lead | 0.0 mg/L 0% of the EPA limit 0.0150 mg/L Main supplier: ST CHARLES COUNTY PWSD 2 · 100,587 people · 2025
Highest in the city: 0.0015 mg/L — OFALLON PWS · 32,515 people · 2025 | 5/5 | LCR |
Each bar shows the measured level as a share of the EPA limit: green is
well under, amber is close to it, red is over. For lead and copper the
limit applies to exactly the 90th-percentile figure shown, so red there
means a real exceedance. For everything else the limit applies to a
running annual average while the figure is the 95th percentile of the
system's samples — over 100% is worth reading, but is not by itself a
violation.
Formal violations are listed separately.
These are the utilities' own EPA-reported results, not a city-wide
average. A detection means the lab measured the
substance — it isn't the same as exceeding a legal limit. Hover a source
tag to see the EPA program and years behind each figure.
Water suppliers serving O'Fallon
| Supplier | Population served |
|---|---|
| ST CHARLES COUNTY PWSD 2 | 100,587 |
| OFALLON PWS | 32,515 |
| ST PAUL PWS | 1,700 |
| ST CHARLES CO PWSD 2 AUGUSTA | 881 |
| ST CHARLES CO PWSD 2 - SUMAC RIDGE | 103 |
Frequently asked questions about O'Fallon tap water
Is O'Fallon tap water safe to drink?
EPA testing detected 27 contaminants in the water serving O'Fallon. A detection isn't the same as a violation — most detected levels are within federal limits. Check the level and source for each contaminant above, and your utility's annual Consumer Confidence Report for the official compliance status.
How many water suppliers serve O'Fallon?
5 public water suppliers report drinking-water monitoring for O'Fallon, Missouri to the EPA. Each is listed above with its population served.
What contaminants are in O'Fallon's water?
The contaminants EPA monitoring detected in O'Fallon include Fluoride, Nitrate-Nitrite, Copper, Barium, TTHM. The full list, with the level at the main supplier and the data source, is in the table above.
Where does this data come from?
Every figure is official EPA drinking-water monitoring — the Lead & Copper Rule, the UCMR-5 nationwide testing program, and the EPA Six-Year Review — not our own testing. Each number is labelled with its source and period.