O'Fallon
MO

Is O'Fallon, MO Tap Water Safe to Drink?

O'Fallon tap water meets federal Safe Drinking Water Act standards but 2 of 2 ZIP codes show detections above EPA health guidelines, primarily for lithium. A certified filter is recommended for households that want an additional layer of protection.

4Water systems
2ZIP codes
100%ZIPs above EPA guideline
Metro areaSt. Louis, MO-IL
Latest data2025-09-15

Where Does O'Fallon Get Its Water?

Water in O'Fallon, MO is provided by 4 public water systems: CLARK COUNTY CONS PWSD 1, OFALLON PWS, ST CHARLES COUNTY PWSD 2 and THOMAS HILL PWSD 1.

How Is O'Fallon Tap Water Treated?

Treated water is disinfected using free chlorine and calcium hypochlorite and chloramines and on-site generated disinfectant. Treatment includes air stripping, conventional treatment (coagulation, flocculation, and filtration), direct filtration, granular activated carbon filtration, groundwater disinfection, ion exchange, in-line filtration, membrane filtration, post-ozone biofiltration and slow sand filtration.

What's in O'Fallon Tap Water?

The following contaminants were detected most frequently in O'Fallon public water systems. 2 of 2 ZIP codes showed detections above EPA health guidelines.

ContaminantPeak detectedEPA guidelineZIPs detectedStatus
lithium 31.2 µg/L 10 µg/L 2 ZIPs Above guideline
PFBA 0.0073 µg/L — 1 ZIP Within guideline
PFTrDA 0.007 µg/L — 0 ZIPs Within guideline
6:2 FTS 0.005 µg/L — 0 ZIPs Within guideline
11Cl-PF3OUdS 0.005 µg/L — 0 ZIPs Within guideline

Health Risk Profile for O'Fallon

Based on EPA monitoring data, 2 of 2 ZIP codes in O'Fallon have recorded detections above EPA health guidelines. Sensitive populations such as infants, pregnant individuals, and those with weakened immune systems may benefit from an additional layer of protection such as a certified point-of-use filter.

Best Broad-Spectrum Filters for This Water Profile

This city profile includes PFAS detections, chlorine disinfection, and other dissolved contaminants. Reverse osmosis (RO) systems certified under NSF/ANSI 58 provide broad reduction coverage; for PFAS specifically, confirm NSF/ANSI P473 or equivalent PFAS reduction certification.

Waterdrop G3P600 Reverse Osmosis System
Under-sink RO system

8-stage tankless RO system certified to NSF/ANSI 58, reduces 1,000+ contaminants including PFAS, lead, arsenic, fluoride, and nitrates.

See recommendations matched to your exact address: choose your ZIP code below.

Frequently Asked Questions about O'Fallon Tap Water

Is O'Fallon tap water safe to drink?

O'Fallon tap water meets Safe Drinking Water Act requirements but 2 of 2 ZIP codes show contaminant levels above EPA health-based guidelines. A certified point-of-use filter adds an extra layer of protection.

What contaminants are in O'Fallon tap water?

The most commonly detected contaminants in O'Fallon water systems include: lithium, PFBA, PFTrDA. See the ZIP-level reports for exact measurements and EPA guideline comparisons.

Where does O'Fallon get its drinking water?

O'Fallon receives water from 4 public water systems, including CLARK COUNTY CONS PWSD 1.

Do I need a water filter in O'Fallon?

If your ZIP code is among those with detections above EPA health guidelines, choose a filter certified for the specific contaminants shown in your ZIP report. Reverse osmosis is generally the broadest option for PFAS, lithium, and many other dissolved contaminants.

How often is O'Fallon tap water tested?

Public water systems in O'Fallon are required by the EPA to test for regulated contaminants on schedules ranging from daily (for microbials and disinfectants) to annual or triennial (for many chemical contaminants). Results are published in annual Consumer Confidence Reports (CCRs). The data on this page reflects the most recent available EPA monitoring results, with the latest sample date of 2025-09-15.

Tap water reports by ZIP in O'Fallon

Water utilities serving O'Fallon, MO

Service area boundaries are approximate and based on state filings or modeled estimates. Contact your utility to confirm exact service at a specific address.

Modeled boundaries are shown with a dashed outline.

Also covers / overlaps with