Public water system · CO0101150

Active

Thornton City of

At a glance

City of Thornton (PWSID CO0101150) is an active community water system in Adams County, Colorado. It reports serving 226,465 people through 42,530 service connections. Its primary water source is surface water, and EPA lists it as owned by a local government. EPA's records list 11 violations for this system; none is health-based, and the most recent began in November 2023.

Dataset updated October 2026 . Source: EPA SDWIS/ECHO public records.

Population served

226,465

Service connections

42,530

Primary source

Surface water

System type

CWS

Community water system

System record

PWSIDCO0101150

System typeCommunity water system

Activity statusActive

Population served226,465

Service connections42,530

Primary water sourceSurface water

Owner typeLocal government

Primacy agencyCO state drinking water program

City served—

StateColorado

ZIP—

CountyAdams County

How does City of Thornton compare with other water systems in Adams County?

By EPA's size categories, City of Thornton is a very large system (more than 100,000 people). Adams County has 82 active public water systems, and City of Thornton is the largest of them by population served. Its population served is about 26 times the county average of 8,669 people per system, and accounts for 32% of the 710,822 people reported by systems filed under the county. Across Colorado, the 2,207 active systems average 3,400 people each. Nationally, the average active community water system reports serving 6,703 people, so City of Thornton is about 34 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. Colorado has 1,068 active community water systems, 48% of the state's 2,207 active systems. Surface water means the system draws its water from rivers, lakes, streams or reservoirs. 228 Colorado systems (10%) list surface water as their primary source.

Who owns and regulates City of Thornton?

EPA lists City of Thornton as owned by a local government. The CO 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 82 active systems in Adams County (23%) are also owned by a local government.

Does City of Thornton have drinking water violations?

EPA's records list 11 violations for this system; none is health-based, and the most recent began in November 2023. The violations listed here began between September 2003 and November 2023. By type: 11 monitoring and reporting. The contaminant or rule involved most often is Interim Enhanced Surface Water Treatment Rule (5 of them). EPA lists 11 as resolved. 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
2023-11-01	Monitoring and reportingMonitoring, Turbidity (Enhanced SWTR) · code 38	Interim Enhanced Surface Water Treatment Rulecode 0300	No	Resolved
2023-10-01	Monitoring and reportingMonitoring, Turbidity (Enhanced SWTR) · code 38	Interim Enhanced Surface Water Treatment Rulecode 0300	No	Resolved
2023-09-01	Monitoring and reportingMonitoring, Turbidity (Enhanced SWTR) · code 38	Interim Enhanced Surface Water Treatment Rulecode 0300	No	Resolved
2023-07-01	Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52	Lead and Copper Rulecode 5000	No	Resolved
2022-04-01	Monitoring and reportingMonitoring, Regular · code 03	Combined Radium (-226 and -228)code 4010	No	Resolved
2022-04-01	Monitoring and reportingMonitoring, Regular · code 03	Combined Uraniumcode 4006	No	Resolved
2022-04-01	Monitoring and reportingMonitoring, Regular · code 03	Gross alpha (excluding radon and uranium)code 4000	No	Resolved
2021-05-01	Monitoring and reportingMonitoring, Turbidity (Enhanced SWTR) · code 38	Interim Enhanced Surface Water Treatment Rulecode 0300	No	Resolved
2010-07-01	Monitoring and reportingWater Quality Parameter M/R · code 53	Lead and Copper Rulecode 5000	No	Resolved
2008-01-01	Monitoring and reportingMonitoring, Regular · code 03	Diquatcode 2032	No	Resolved
2003-09-01	Monitoring and reportingMonitoring, Turbidity (Enhanced SWTR) · code 38	Interim Enhanced Surface Water Treatment Rulecode 0300	No	Resolved

All 11 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.

City of Thornton: frequently asked questions

Who runs City of Thornton?

City of Thornton (PWSID CO0101150) is a community water system owned by a local government. It is regulated by the CO state drinking water program.

How many people does City of Thornton serve?

City of Thornton reports serving 226,465 people through 42,530 service connections in Adams County, Colorado.

Where does City of Thornton get its water?

EPA SDWIS lists this system's primary water source as surface water. Surface water means the system draws its water from rivers, lakes, streams or reservoirs.

Does City of Thornton have any drinking water violations?

EPA's records list 11 violations for this system; none is health-based, and the most recent began in November 2023. 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 City of Thornton'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 11 violations for this system; none is health-based, and the most recent began in November 2023. For current results, consult the system's annual water quality report, EPA ECHO, or the CO state drinking water program.

Where can I find City of Thornton's water quality report?

As a community water system, City of Thornton 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 Adams County

Water system	County	Population served	Type	Source
Westminster City of	Adams	202,078	Community	Surface water
South Adams County Wsd	Adams	75,559	Community	Purchased surface water
Brighton City of	Adams	56,304	Community	Purchased surface water
Northglenn City of	Adams	48,927	Community	Surface water
Crestview Wsd	Adams	23,756	Community	Purchased surface water
North Washington Street Wsd	Adams	14,500	Community	Purchased surface water

Working with water-system records? Pro adds alerts, change history and CSV export ($49/mo); Enterprise adds full national files, the API and an MCP server for AI tools.

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 City of, PWSID CO0101150, Colorado”, https://aquacensus.com/water-systems/colorado/thornton-city-of-co0101150 (data as of October 1, 2026).