Public water system · IL0991050
ActiveSeneca
At a glance
Seneca (PWSID IL0991050) is an active community water system in LaSalle County, Illinois. It reports serving 2,353 people through 896 service connections. Its primary water source is groundwater, 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 September 2015.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
2,353
Service connections
896
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does Seneca compare with other water systems in LaSalle County?
By EPA's size categories, Seneca is a small system (501 to 3,300 people). LaSalle County has 129 active public water systems. Its population served is about 188% above the county average of 816 people per system, and accounts for 2.2% of the 105,319 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 Seneca is about 65% below 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. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 2,808 Illinois systems (73%) list groundwater as their primary source.
Who owns and regulates Seneca?
EPA lists Seneca 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. 20 of the 129 active systems in LaSalle County (16%) are also owned by a local government.
Does Seneca have drinking water violations?
Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in September 2015. The violations listed here began between August 1993 and September 2015. By type: 6 monitoring and reporting and 6 contaminant level above the legal limit. The contaminant or rule involved most often is Combined Radium (-226 and -228) (8 of them). EPA lists 10 as resolved and 2 as archived. 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. 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.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2015-09-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Total trihalomethanes (TTHM)code 2950 | No | Resolved |
| 2015-09-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Haloacetic acids (HAA5)code 2456 | No | Resolved |
| 2005-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Combined Radium (-226 and -228)code 4010 | Yes | Resolved |
| 2005-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Combined Radium (-226 and -228)code 4010 | Yes | Resolved |
| 2005-04-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Combined Radium (-226 and -228)code 4010 | Yes | Resolved |
| 2005-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Combined Radium (-226 and -228)code 4010 | Yes | Resolved |
| 2004-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Combined Radium (-226 and -228)code 4010 | Yes | Resolved |
| 2003-07-01 | Monitoring and reportingMonitoring, Regular · code 03 | Combined Radium (-226 and -228)code 4010 | No | Resolved |
| 2003-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Combined Radium (-226 and -228)code 4010 | No | Resolved |
| 2000-09-07 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Combined Radium (-226 and -228)code 4010 | Yes | Resolved |
| 1994-07-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1993-08-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | 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.
Seneca: frequently asked questions
Who runs Seneca?
Seneca (PWSID IL0991050) is a community water system owned by a local government. It is regulated by the IL state drinking water program.
How many people does Seneca serve?
Seneca reports serving 2,353 people through 896 service connections in LaSalle County, Illinois.
Where does Seneca get its water?
EPA SDWIS lists this system's primary water source as groundwater. Groundwater means the system draws its water from wells or springs fed by underground aquifers.
Does Seneca 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 September 2015. 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 Seneca'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 September 2015. For current results, consult the system's annual water quality report, EPA ECHO, or the IL state drinking water program.
Where can I find Seneca's water quality report?
As a community water system, Seneca 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 LaSalle County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Il American-Streator | LaSalle | 19,000 | Community | Surface water |
| Ottawa | LaSalle | 18,097 | Community | Groundwater |
| Peru | LaSalle | 10,300 | Community | Groundwater |
| La Salle | LaSalle | 9,700 | Community | Groundwater |
| Mendota | LaSalle | 7,100 | Community | Groundwater |
| Marseilles | LaSalle | 5,061 | Community | Groundwater |
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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, “Seneca, PWSID IL0991050, Illinois”, https://aquacensus.com/water-systems/illinois/seneca-il0991050 (data as of October 1, 2026).