Is O Fallon, MO Tap Water Safe to Drink?
Graded F — but Strontium and Chlorate were detected above EPA limits. Here's what's in the water and how to remove it. What to do next ↓
43.4/100
waterverge.com O Fallon, MO — Water Quality Report
O Fallon's drinking water received a grade of F (43.4 out of 100), indicating failing water quality. The city's 9 water systems serve approximately 138,108 residents using purchased surface water.
Lead levels were measured at 1.5 ppb (90th percentile), well within EPA limits. UCMR 5 testing detected 3 PFAS compounds in the water supply.
The system has 86 violations on record, including 10 health-based violations. 20 remain unresolved.
What to know about O Fallon's water
O Fallon ranks #499 out of 509 cities in Missouri for water quality, placing it among the lowest-rated in the state.
The city draws from surface water sources, which are more susceptible to seasonal runoff and agricultural contamination, requiring extensive multi-barrier treatment including coagulation, filtration, and disinfection.
PFAS compounds were detected in testing, though levels remain within current EPA limits. Residents seeking extra precaution may consider an activated carbon or reverse osmosis filter.
Hexavalent chromium (chromium-6) was detected at 2.40 µg/L in UCMR 3 testing. While below California's 10 µg/L limit and with no federal MCL set, residents sensitive to this contaminant may consider reverse osmosis filtration.
The system has seen 51 violations in the past five years, suggesting a pattern of compliance challenges that residents should monitor closely.
Water quality score
See methodology →Is O Fallon, MO water safe to drink?
O Fallon's drinking water has significant quality concerns based on EPA testing data. With a grade of F (43.4/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 9 water systems serve approximately 138,108 residents using surface water (rivers, lakes, or reservoirs).
Recent water quality updates for O Fallon
A timeline of significant water quality events, violations, and data updates.
Detected at levels within current EPA limits. PFAS persist indefinitely in the environment.
Latest EPA compliance and testing data incorporated into O Fallon's water quality assessment. Grade: F (43.4/100).
Contaminants: Revised Total Coliform Rule, Consumer Confidence Rule.
Contaminants: Groundwater Rule, Revised Total Coliform Rule.
Contaminants: Revised Total Coliform Rule.
Key contaminant findings
Based on the most recent EPA sampling data for O Fallon's water supply.
Well within EPA limits.
Detected but within current EPA limits. PFAS do not break down in the environment and can accumulate in the body over time. An activated carbon filter can reduce exposure.
PFAS "forever chemicals" detected
UCMR 5 testing found 3 PFAS compounds in O Fallon's water supply. PFAS are synthetic chemicals that persist indefinitely in the environment and the human body.
Violation history
O Fallon's water system has 86 total violations on record, including 10 health-based violations. 20 remain unresolved. 51 violations were issued in the last 5 years.
Where does O Fallon's water come from?
O Fallon's drinking water comes from surface water (rivers, lakes, or reservoirs), supplied by 9 water systems serving approximately 138,108 people. Surface water sources are more susceptible to contamination from runoff, industrial discharge, and algal blooms, requiring extensive treatment. Nearby water bodies include Cuivre River At Old Monroe (river), Dardenne Creek At O'Fallon (river), Dardenne Creek At Old Town St. Peters (river), Bonhomme Creek Near Clarkson Valley (river), Caulks Creek At Chesterfield (river).
What O Fallon residents can do
Recommended: Activated carbon or reverse osmosis filter. This addresses the specific contaminants found in O Fallon's water.
Your water utility is required to publish an annual Consumer Confidence Report (CCR) with detailed testing results. Ask for the latest copy or check your utility's website.
Data: EPA SDWIS, UCMR 5 (PFAS), FEMA, NOAA. Last updated May 2026.
Top contaminants to know
View all ↓Forever chemicals overview
National PFAS report →Violation summary
Violations & advisories
Recommended water filters
Based on contaminants detected in O Fallon's water supply, we recommend the following filter types.
Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| Lead (90th percentile) LeadHeavy Metal A toxic heavy metal that can leach into drinking water from older pipes, solder, and fixtures. No amount of lead in water is considered safe. Health EffectsBrain and nervous system damage in children, kidney damage, high blood pressure, and reproductive problems in adults. EPA Limit15 ppb action level Common SourcesCorrosion of lead pipes, lead solder, brass faucets, and household plumbing. | 1.5 | 15 | ppb | Inorganic | Safe |
| 11Cl-PF3OUdS | ND | HI | µg/L | PFAS | Not Detected |
| 4:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 6:2 FTS 6:2 FTSPFAS A fluorotelomer sulfonate commonly found at sites contaminated with aqueous film-forming foam (AFFF) used in firefighting. Health EffectsPotential liver toxicity and endocrine disruption. Less studied but identified as a contaminant of concern. EPA LimitNo individual MCL (not yet regulated) Common SourcesFirefighting foam (AFFF), airports, military bases, and industrial facilities. | ND | HI | µg/L | PFAS | Not Detected |
| 8:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 9Cl-PF3ONS | ND | HI | µg/L | PFAS | Not Detected |
| ADONA | ND | HI | µg/L | PFAS | Not Detected |
| HFPO-DA HFPO-DA (GenX)PFAS A replacement for PFOA in manufacturing, marketed as safer but still a persistent "forever chemical." Also known as GenX. Health EffectsLiver and kidney effects, reproductive toxicity, immune system effects, and potential cancer risk. EPA Limit10 ppt MCL Common SourcesFluoropolymer manufacturing (used as PFOA replacement), industrial wastewater discharge. | ND | 0.01 | µg/L | PFAS | Not Detected |
| lithium LithiumInorganic A naturally occurring alkali metal found in groundwater. Monitored under UCMR 5 to assess occurrence in drinking water. Health EffectsKidney effects at high doses. Low-level exposure effects under study; some research suggests neurological effects. EPA LimitNo MCL (monitoring only under UCMR 5) Common SourcesNatural mineral deposits, geothermal water, and industrial discharge. | 71.300 | HI | µg/L | PFAS | Detected |
| NEtFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| NFDHA | ND | HI | µg/L | PFAS | Not Detected |
| NMeFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| PFBA PFBAPFAS One of the shortest-chain PFAS compounds. Very mobile in water and difficult to remove with standard filtration. Health EffectsThyroid effects, potential developmental toxicity. Shorter half-life in body than long-chain PFAS. EPA LimitNo individual MCL (not yet regulated) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and firefighting foam. | 0.006 | HI | µg/L | PFAS | Detected |
| PFBS PFBSPFAS A short-chain PFAS used as a replacement for PFOS. While it clears the body faster than long-chain PFAS, it still persists in the environment. Health EffectsThyroid effects, reproductive and developmental toxicity, kidney effects. EPA LimitPart of Hazard Index (1.0) Common SourcesIndustrial discharge, firefighting foam, and as a replacement chemical in manufacturing. | ND | HI | µg/L | PFAS | Not Detected |
| PFDA | ND | HI | µg/L | PFAS | Not Detected |
| PFDoA | ND | HI | µg/L | PFAS | Not Detected |
| PFEESA | ND | HI | µg/L | PFAS | Not Detected |
| PFHpA PFHpAPFAS A medium-chain PFAS compound found in various environmental samples. Less studied than PFOA/PFOS but still considered a contaminant of concern. Health EffectsLiver effects, potential developmental toxicity, and endocrine disruption. EPA LimitPart of Hazard Index (1.0) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and contaminated water sources. | ND | HI | µg/L | PFAS | Not Detected |
| PFHpS | ND | HI | µg/L | PFAS | Not Detected |
| PFHxA PFHxAPFAS A short-chain PFAS replacement chemical widely used after manufacturers phased out longer-chain PFAS. Very commonly detected in water. Health EffectsLiver and kidney effects, potential thyroid disruption. Considered less toxic than long-chain PFAS but still persistent. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial processes, firefighting foam (AFFF), food packaging, and textile treatment. | ND | HI | µg/L | PFAS | Not Detected |
| PFHxS PFHxSPFAS A medium-chain PFAS found in firefighting foam and consumer products. It has a long half-life in the human body, similar to long-chain PFAS. Health EffectsImmune system effects, thyroid disruption, and potential reproductive and developmental harm. EPA LimitPart of Hazard Index (1.0) Common SourcesFirefighting foam (AFFF), waterproof textiles, food packaging, and industrial discharge. | ND | HI | µg/L | PFAS | Not Detected |
| PFMBA | ND | HI | µg/L | PFAS | Not Detected |
| PFMPA | ND | HI | µg/L | PFAS | Not Detected |
| PFNA PFNAPFAS A long-chain PFAS compound used in manufacturing fluoropolymers. It bioaccumulates in the body and is very persistent in the environment. Health EffectsDevelopmental effects, liver toxicity, immune suppression, and potential cancer risk. EPA LimitPart of Hazard Index (1.0) Common SourcesFluoropolymer manufacturing, industrial emissions, and contaminated water sources. | ND | HI | µg/L | PFAS | Not Detected |
| PFOA PFOAPFAS A long-chain PFAS ("forever chemical") once widely used in nonstick coatings and firefighting foam. It persists in the body and environment for years. Health EffectsLinked to kidney and testicular cancer, thyroid disease, elevated cholesterol, and reproductive issues. EPA Limit4.0 ppt MCL Common SourcesIndustrial discharge, firefighting foam (AFFF), nonstick cookware manufacturing, and contaminated groundwater. | ND | 0.004 | µg/L | PFAS | Not Detected |
| PFOS PFOSPFAS A long-chain PFAS compound historically used in stain-resistant coatings and firefighting foam. One of the most studied and persistent PFAS chemicals. Health EffectsLiver damage, immune system suppression, thyroid disruption, increased cholesterol, and potential cancer risk. EPA Limit4.0 ppt MCL Common SourcesFirefighting foam (AFFF), industrial sites, stain-resistant fabric treatments, and contaminated groundwater. | ND | 0.004 | µg/L | PFAS | Not Detected |
| PFPeA PFPeAPFAS A short-chain PFAS compound commonly detected in drinking water. One of the most frequently found PFAS in UCMR 5 monitoring. Health EffectsLess studied than PFOA/PFOS. Potential liver and thyroid effects. Research is ongoing. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial discharge, firefighting foam degradation, and consumer products. | 0.003 | HI | µg/L | PFAS | Detected |
| PFPeS | ND | HI | µg/L | PFAS | Not Detected |
| PFTA | ND | HI | µg/L | PFAS | Not Detected |
| PFTrDA | ND | HI | µg/L | PFAS | Not Detected |
| PFUnA | ND | HI | µg/L | PFAS | Not Detected |
Lead level trend (90th percentile)
See how O Fallon compares by contaminant
Explore where O Fallon ranks among all Missouri cities for specific contaminants.
Water source & infrastructure
Where O Fallon's water comes from
O Fallon's drinking water comes primarily from surface water sources such as rivers, lakes, or reservoirs.
Surface water systems require multi-stage treatment including coagulation, sedimentation, filtration, and disinfection to meet EPA Safe Drinking Water Act standards.
These sources can be impacted by seasonal changes, stormwater runoff, upstream agriculture, and industrial discharge.
The system is operated by local government ownership and serves approximately 138,108 people through 9 water systems.
Water bodies near O Fallon
O Fallon is located near 5 notable water bodies. As a surface water system, these water bodies may directly influence the city's drinking water supply.
Water systems serving O Fallon
| System Name | PWSID | Population | Source |
|---|---|---|---|
| ST CHARLES COUNTY PWSD 2 | MO6024530 | 100,587 | SWP |
| OFALLON PWS | MO6010588 | 32,515 | SWP |
| ST PAUL PWS | MO6011535 | 1,700 | GW |
| ST CHARLES COUNTY PWSD 2 WARREN | MO6024629 | 1,192 | GW |
| ST CHARLES CO PWSD 2 AUGUSTA | MO6024531 | 881 | GW |
| ST CHARLES COUNTY PWSD 2 NORTH OAK DR | MO6021633 | 660 | GW |
| ST CHARLES COUNTY PWSD 2 DUTZOW | MO6024628 | 400 | GW |
| ST CHARLES CO PWSD 2 - SUMAC RIDGE | MO6031209 | 103 | GW |
| FENNEC FOX WAY LLC | MO6036061 | 70 | GW |
How O Fallon compares
Full Missouri rankings →O Fallon's score of 43.4/100 is below the average of 67/100 among major Missouri cities. It outscores 3 of 10 nearby cities. 7 of 10 nearby cities score higher.
Nearby cities
View Missouri rankings →Learn more about your water
Guides and resources related to O Fallon's water quality findings.
Explore water quality across St. Charles
Frequently asked questions
Is O Fallon, MO tap water safe to drink?
O Fallon's water quality earned a grade of F (43.4/100). Significant issues have been found. A water filter is strongly recommended. The city ranks #499 out of 509 cities tested in Missouri.
What contaminants are in O Fallon's water?
Lead was measured at 1.5 ppb (90th percentile). 3 PFAS compounds were detected. 86 violations are on record.
How is O Fallon's water quality grade calculated?
The grade is based on four factors: violation history (40%), lead and copper levels (25%), PFAS contamination (25%), and regulatory compliance (10%). The score is also adjusted based on how complete the available data is. See our methodology page for full details.
Do I need a water filter in O Fallon?
PFAS compounds have been detected. A filter with activated carbon can help reduce exposure.
Where does O Fallon's water come from?
O Fallon's water is sourced from Purchased surface water. The city has 9 water systems serving approximately 138,108 residents.
What health violations has O Fallon's water system had?
O Fallon has 10 health-based violations on record. The most recent violation was recorded in July 2025. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 20 violations remain unresolved.
Why does O Fallon have so many PFAS compounds in its water?
3 different PFAS "forever chemical" compounds were detected in O Fallon's water supply during UCMR 5 testing. PFAS contamination often originates from proximity to military installations (AFFF firefighting foam), airports, industrial manufacturing sites, or wastewater treatment facilities. While detected, current levels are within EPA limits. An activated carbon filter can further reduce exposure.
How does O Fallon's water compare to other cities?
O Fallon ranks #499 out of 509 cities in Missouri (better than 2% of state cities) and #14574 out of 15744 cities nationally (7th percentile). The grade of F reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.