Public water system · IA1781019
ActiveThornton Water Supply
At a glance
Thornton Water Supply (PWSID IA1781019) is an active community water system in Cerro Gordo County, Iowa. It reports serving 400 people through 219 service connections. Its primary water source is groundwater, and EPA lists it as owned by a local government. EPA's records list 10 violations for this system; 1 is health-based, and the most recent began in April 2025.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
400
Service connections
219
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does Thornton Water Supply compare with other water systems in Cerro Gordo County?
By EPA's size categories, Thornton Water Supply is a very small system (500 people or fewer). Cerro Gordo County has 34 active public water systems, and Thornton Water Supply is the 5th-largest of them by population served. Its population served is about 66% below the county average of 1,173 people per system, and accounts for 1% of the 39,879 people reported by systems filed under the county. Across Iowa, the 1,828 active systems average 1,718 people each. Nationally, the average active community water system reports serving 6,703 people, so Thornton Water Supply 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. Iowa has 1,084 active community water systems, 59% of the state's 1,828 active systems. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 1,502 Iowa systems (82%) list groundwater as their primary source.
Who owns and regulates Thornton Water Supply?
EPA lists Thornton Water Supply as owned by a local government. The IA state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 11 of the 34 active systems in Cerro Gordo County (32%) are also owned by a local government.
Does Thornton Water Supply have drinking water violations?
EPA's records list 10 violations for this system; 1 is health-based, and the most recent began in April 2025. The violations listed here began between October 1994 and April 2025. By type: 9 monitoring and reporting and 1 contaminant level above the legal limit. The contaminant or rule involved most often is Nitrate (5 of them). EPA lists 9 as resolved and 1 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 |
|---|---|---|---|---|
| 2025-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Archived |
| 2001-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Arseniccode 1005 | No | Resolved |
| 2001-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Arseniccode 1005 | No | Resolved |
| 1996-09-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 1996-09-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 1995-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 1995-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 1995-09-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitritecode 1041 | No | Resolved |
| 1995-09-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitritecode 1041 | No | Resolved |
| 1994-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
All 10 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.
Thornton Water Supply: frequently asked questions
Who runs Thornton Water Supply?
Thornton Water Supply (PWSID IA1781019) is a community water system owned by a local government. It is regulated by the IA state drinking water program.
How many people does Thornton Water Supply serve?
Thornton Water Supply reports serving 400 people through 219 service connections in Cerro Gordo County, Iowa.
Where does Thornton Water Supply 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 Thornton Water Supply have any drinking water violations?
EPA's records list 10 violations for this system; 1 is health-based, and the most recent began in April 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 Thornton Water Supply'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. EPA's records list 10 violations for this system; 1 is health-based, and the most recent began in April 2025. For current results, consult the system's annual water quality report, EPA ECHO, or the IA state drinking water program.
Where can I find Thornton Water Supply's water quality report?
As a community water system, Thornton Water Supply 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 Cerro Gordo County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Mason City Water Department | Cerro Gordo | 27,338 | Community | Groundwater |
| Clear Lake Water Department | Cerro Gordo | 7,687 | Community | Groundwater |
| Rockwell Water Supply | Cerro Gordo | 1,071 | Community | Groundwater |
| Ventura Water Works | Cerro Gordo | 716 | Community | Groundwater |
| Plymouth Water Supply | Cerro Gordo | 378 | Community | Groundwater |
| Bell Harbor | Cerro Gordo | 352 | Transient non-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, “Thornton Water Supply, PWSID IA1781019, Iowa”, https://aquacensus.com/water-systems/iowa/thornton-water-supply-ia1781019 (data as of October 1, 2026).