Tap Water Quality Report
Tap water quality in O'FALLON, Missouri
Tap water in O'FALLON, Missouri receives a grade of D (65/100) from TapWaterSafety.org. It's served by ST CHARLES COUNTY PWSD 2. The most significant water quality concerns are: Haloacetic acids (HAA9) significantly above health guideline; Arsenic* significantly above health guideline; Total trihalomethanes (TTHMs) significantly above health guideline. Data sources: EPA SDWIS, EPA ECHO, EWG Tap Water Database.
What's in O'FALLON's tap water
Top water quality concerns identified by the EPA and Environmental Working Group across the utility serving O'FALLON.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 24.0 ppb, 399x above the EWG health guideline of 0.06 ppb.
Arsenic* significantly above health guideline
Moderate concernArsenic* detected at 0.736 ppb, 184x above the EWG health guideline of 0.004 ppb.
Total trihalomethanes (TTHMs) significantly above health guideline
Moderate concernTotal trihalomethanes (TTHMs) detected at 24.9 ppb, 166x above the EWG health guideline of 0.15 ppb.
EPA compliance record
Official U.S. EPA records for ST CHARLES COUNTY PWSD 2 (system ID MO6024530) for the last 3 years. Checked 2026-10-07.
| Rule | Type | Since | Status |
|---|---|---|---|
| Ground Water Rule | Missed testing or reporting | 06/01/2025 | Open |
Source: U.S. EPA Enforcement and Compliance History Online (ECHO), from the Safe Drinking Water Information System. See EPA's full report.
Recommended filters for O'FALLON
Filters matched to the specific contaminants in O'FALLON's water supply.
Carbon filter certified for VOCs (NSF/ANSI 53)
$180-$599Activated carbon is effective for disinfection byproducts. Look for NSF/ANSI 53 VOC reduction.
Reverse osmosis certified for arsenic (NSF/ANSI 58)
$429-$599Reverse osmosis certified under NSF/ANSI 58 for arsenic is the most reliable home option.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
All contaminants detected in O'FALLON's tap water
Every contaminant identified, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal. Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Haloacetic acids (HAA9) Disinfection byproduct |
24.0 ppb | 0.06 | — | — | — | — | — | 399× over |
| Arsenic* Heavy metal |
0.736 ppb | 0.004 | 10.0 | 10 | 10 | 0.004 | — | 184× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
24.9 ppb | 0.15 | 80.0 | 100 | — | — | — | 166× over |
| Haloacetic acids (HAA5) Disinfection byproduct |
14.1 ppb | 0.1 | 60.0 | 60 | — | — | — | 141× over |
| Bromochloroacetic acid* Disinfection byproduct |
2.03 ppb | 0.02 | — | — | — | — | — | 102× over |
| Bromodichloromethane Disinfection byproduct |
6.02 ppb | 0.06 | — | — | — | — | — | 100× over |
| Chromium (hexavalent) Heavy metal |
1.36 ppb | 0.02 | — | — | — | — | — | 68× over |
| Dichloroacetic acid Disinfection byproduct |
10.4 ppb | 0.2 | — | — | — | — | — | 52× over |
| Chloroform Disinfection byproduct |
15.6 ppb | 0.4 | — | — | — | — | — | 39× over |
| Radium, combined (-226 and -228) Radiological |
1.75 pCi/L | 0.05 | 5.0 | — | — | — | — | 35× over |
| Trichloroacetic acid Disinfection byproduct |
2.9 ppb | 0.1 | — | — | — | — | — | 29× over |
| Dibromoacetic acid Disinfection byproduct |
0.794 ppb | 0.03 | — | — | — | — | — | 26× over |
| Dibromochloromethane Disinfection byproduct |
2.63 ppb | 0.1 | — | — | — | — | — | 26× over |
| Nitrate* Inorganic |
1.02 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 7.3× over |
| Atrazine* Pesticide/Herbicide |
0.2 ppb | 0.1 | 3.0 | 0.1 | 100 | 0.15 | — | Fails EU |
| Nitrate and nitrite Inorganic |
0.164 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 1.2× over |
| Chlorate Disinfection byproduct |
207.1 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Bromoform Disinfection byproduct |
0.247 ppb | 0.5 | — | — | — | — | — | Below guideline |
| Antimony* Heavy metal |
0.315 ppb | 1.0 | 6.0 | 10 | 20 | 1 | — | Below guideline |
| Barium Heavy metal |
65.0 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| 1,4-Dioxane* Semi-volatile organic compound |
0.0288 ppb | 0.35 | — | — | 50 | 1 | — | Below guideline |
| Vanadium Other |
1.44 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Molybdenum Other |
2.63 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Selenium* Heavy metal |
1.64 ppb | 30.0 | 50.0 | 20 | 40 | 30 | — | Below guideline |
| Manganese Heavy metal |
4.95 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Monochloroacetic acid* Disinfection byproduct |
2.41 ppb | 53.0 | — | — | — | — | — | Below guideline |
| Monobromoacetic acid* Disinfection byproduct |
0.157 ppb | 25.0 | — | — | — | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA) PFAS |
5.85 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Aluminum* Heavy metal |
2.15 ppb | 600.0 | — | 200 | — | 600 | — | Below guideline |
| Strontium Radiological |
0.213 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Chlorodifluoromethane Other |
0.0238 ppb | — | — | — | — | — | — | Below guideline |
| Chromium (total)* Heavy metal |
1.38 ppb | — | 100.0 | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.554 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| Lithium Other |
24.6 ppb | — | — | — | — | — | — | Below guideline |
| Nitrite* Inorganic |
0.0263 ppm | — | 1.0 | — | — | — | — | Below guideline |
| o-toluidine Other |
0.00138 ppb | — | — | — | — | — | — | Below guideline |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines, California OEHHA PHGs, EWG Tap Water Database.
Treatment plant contact info
For service issues, water quality concerns, or to request a Consumer Confidence Report from ST CHARLES COUNTY PWSD 2.