Public water system · WI6630259
ActiveOntario Waterworks
At a glance
Ontario Waterworks (PWSID WI6630259) is an active community water system in Vernon County, Wisconsin. It reports serving 554 people through 241 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, 5 are health-based, and the most recent began in July 2025.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
554
Service connections
241
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does Ontario Waterworks compare with other water systems in Vernon County?
By EPA's size categories, Ontario Waterworks is a small system (501 to 3,300 people). Vernon County has 66 active public water systems. Its population served is about twice the county average of 255 people per system, and accounts for 3.3% of the 16,796 people reported by systems filed under the county. Across Wisconsin, the 11,056 active systems average 469 people each. Nationally, the average active community water system reports serving 6,703 people, so Ontario Waterworks is well 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. Wisconsin has 1,053 active community water systems, 9.5% of the state's 11,056 active systems. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 10,978 Wisconsin systems (99%) list groundwater as their primary source.
Who owns and regulates Ontario Waterworks?
EPA lists Ontario Waterworks as owned by a local government. The WI state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 19 of the 66 active systems in Vernon County (29%) are also owned by a local government.
Does Ontario Waterworks have drinking water violations?
Of the 12 most recent violations in EPA's records, 5 are health-based, and the most recent began in July 2025. The violations listed here began between October 1997 and July 2025. By type: 5 monitoring and reporting, 4 contaminant level above the legal limit, 1 monitoring, 1 required treatment not met and 1 public notice, recordkeeping or other. The contaminant or rule involved most often is Total coliform bacteria (TCR) (6 of them). EPA lists 9 as resolved, 2 as archived and 1 as unaddressed. 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. Unaddressed means the violation is not resolved or archived and is not yet covered by formal enforcement.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2025-07-01 | MonitoringMonitoring, Routine (RTCR) · code 3A | Revised Total Coliform Rulecode 8000 | No | Resolved |
| 2025-01-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Haloacetic acids (HAA5)code 2456 | No | Archived |
| 2025-01-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Total trihalomethanes (TTHM)code 2950 | No | Archived |
| 2024-10-17 | Required treatment not metLSL Inventory · code 2E | Lead and Copper Rule Revisionscode 5200 | Yes | Resolved |
| 2024-10-17 | Public notice, recordkeeping or otherPublic Notification Violation for NPDWR Violation · code 75 | Public Noticecode 7500 | No | Unaddressed |
| 2009-04-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 2009-04-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Chlorinecode 0999 | No | Resolved |
| 2006-06-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2001-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1998-06-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1998-05-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1997-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
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.
Ontario Waterworks: frequently asked questions
Who runs Ontario Waterworks?
Ontario Waterworks (PWSID WI6630259) is a community water system owned by a local government. It is regulated by the WI state drinking water program.
How many people does Ontario Waterworks serve?
Ontario Waterworks reports serving 554 people through 241 service connections in Vernon County, Wisconsin.
Where does Ontario Waterworks 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 Ontario Waterworks have any drinking water violations?
Of the 12 most recent violations in EPA's records, 5 are health-based, and the most recent began in July 2025. 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 Ontario Waterworks' 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, 5 are health-based, and the most recent began in July 2025. For current results, consult the system's annual water quality report, EPA ECHO, or the WI state drinking water program.
Where can I find Ontario Waterworks' water quality report?
As a community water system, Ontario Waterworks 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 Vernon County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Viroqua Waterworks | Vernon | 4,362 | Community | Groundwater |
| Westby Waterworks | Vernon | 2,400 | Community | Groundwater |
| Hillsboro Waterworks | Vernon | 1,325 | Community | Groundwater |
| Stoddard Waterworks | Vernon | 793 | Community | Groundwater |
| Coon Valley Waterworks | Vernon | 765 | Community | Groundwater |
| La Farge Waterworks | Vernon | 712 | 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, “Ontario Waterworks, PWSID WI6630259, Wisconsin”, https://aquacensus.com/water-systems/wisconsin/ontario-waterworks-wi6630259 (data as of October 1, 2026).