Public water system · IL1631100
ActiveO Fallon
At a glance
O Fallon (PWSID IL1631100) is an active community water system in St. Clair County, Illinois. It reports serving 46,603 people through 18,497 service connections. Its primary water source is purchased surface water, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2026.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
46,603
Service connections
18,497
Primary source
SWP
Purchased surface water
System type
CWS
Community water system
System record
How does O Fallon compare with other water systems in St. Clair County?
By EPA's size categories, O Fallon is a large system (10,001 to 100,000 people). St. Clair County has 42 active public water systems, and O Fallon is the 2nd-largest of them by population served. Its population served is about 7.7 times the county average of 6,082 people per system, and accounts for 18% of the 255,459 people reported by systems filed under the county. Across Illinois, the 3,872 active systems average 3,204 people each. Nationally, the average active community water system reports serving 6,703 people, so O Fallon is about 7 times that figure.
What does “community water system” mean?
A community water system serves at least 15 connections used by year-round residents, or regularly serves at least 25 year-round residents. Homes, apartments and mobile-home parks are served by these. Illinois has 1,773 active community water systems, 46% of the state's 3,872 active systems. Purchased surface water means the system buys surface water from another public water system rather than drawing its own. 619 Illinois systems (16%) list purchased surface water as their primary source.
Who owns and regulates O Fallon?
EPA lists O Fallon as owned by a local government. The IL state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 22 of the 42 active systems in St. Clair County (52%) are also owned by a local government.
Does O Fallon have drinking water violations?
Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2026. The violations listed here began between November 1995 and January 2026. By type: 6 monitoring and reporting and 6 contaminant level above the legal limit. The contaminant or rule involved most often is Total coliform bacteria (TCR) (7 of them). EPA lists 9 as archived and 3 as resolved. Archived means the violation was not marked resolved but is more than five years past the end of the noncompliance period, so it no longer counts toward current compliance status. Resolved means at least one resolving action is on record: the system returned to compliance, the rule no longer applies, or no further action was needed.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2026-01-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Total trihalomethanes (TTHM)code 2950 | No | Archived |
| 2026-01-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Haloacetic acids (HAA5)code 2456 | No | Archived |
| 2007-01-01 | Monitoring and reportingWater Quality Parameter M/R · code 53 | Lead and Copper Rulecode 5000 | No | Resolved |
| 1999-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Archived |
| 1999-07-01 | Monitoring and reportingMonitoring, Repeat Minor (TCR) · code 26 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1998-04-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Acute (TCR) · code 21 | Total coliform bacteria (TCR)code 3100 | Yes | Archived |
| 1998-04-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Archived |
| 1997-04-01 | Monitoring and reportingWater Quality Parameter M/R · code 53 | Lead and Copper Rulecode 5000 | No | Resolved |
| 1997-01-01 | Monitoring and reportingWater Quality Parameter M/R · code 53 | Lead and Copper Rulecode 5000 | No | Resolved |
| 1996-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Archived |
| 1996-03-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Archived |
| 1995-11-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Archived |
The 12 most recent violations in EPA's records, newest first.Labels and codes come from EPA's SDWIS reference tables. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found. "Health-based" marks violations of a legal limit or required treatment.
O Fallon: frequently asked questions
Who runs O Fallon?
O Fallon (PWSID IL1631100) is a community water system owned by a local government. It is regulated by the IL state drinking water program.
How many people does O Fallon serve?
O Fallon reports serving 46,603 people through 18,497 service connections in St. Clair County, Illinois.
Where does O Fallon get its water?
EPA SDWIS lists this system's primary water source as purchased surface water. Purchased surface water means the system buys surface water from another public water system rather than drawing its own.
Does O Fallon have any drinking water violations?
Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2026. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found.
Is O Fallon's water safe to drink?
AquaCensus shows EPA compliance records, not current water test results, so it cannot say whether the water is safe at a given moment. Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2026. For current results, consult the system's annual water quality report, EPA ECHO, or the IL state drinking water program.
Where can I find O Fallon's water quality report?
As a community water system, O Fallon must deliver an annual water quality report, called a Consumer Confidence Report, to its customers by July 1 each year, covering the previous calendar year. The system can provide a copy on request.
Other water systems in St. Clair County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Il American-East St Louis | St. Clair | 131,368 | Community | Surface water |
| Caseyville | St. Clair | 13,798 | Community | Purchased surface water |
| Cahokia Heights | St. Clair | 12,528 | Community | Purchased surface water |
| Mascoutah | St. Clair | 8,759 | Community | Purchased surface water |
| American Water Oper and Maintenance, LLC | St. Clair | 6,779 | Community | Purchased surface water |
| Lebanon | St. Clair | 4,714 | Community | Purchased surface water |
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About this data
Source: U.S. EPA Safe Drinking Water Information System (SDWIS) and SDWA violation records, via EPA ECHO, as published October 1, 2026 — AquaCensus refreshes it quarterly. See the methodology for how records are matched, cleaned and scored.
Cite as: AquaCensus, “O Fallon, PWSID IL1631100, Illinois”, https://aquacensus.com/water-systems/illinois/o-fallon-il1631100 (data as of October 1, 2026).