Public water system · WY5600036
ActiveMills, City of
At a glance
City of Mills (PWSID WY5600036) is an active community water system in Natrona County, Wyoming. It reports serving 4,050 people through 2,209 service connections. Its primary water source is groundwater under influence of surface water, and EPA lists it as owned by a local government. EPA's records list 8 violations for this system; 3 are health-based, and the most recent began in January 2025.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
4,050
Service connections
2,209
Primary source
GU
Groundwater under influence of surface water
System type
CWS
Community water system
System record
How does City of Mills compare with other water systems in Natrona County?
By EPA's size categories, City of Mills is a medium system (3,301 to 10,000 people). Natrona County has 48 active public water systems, and City of Mills is the 2nd-largest of them by population served. Its population served is about 141% above the county average of 1,680 people per system, and accounts for 5% of the 80,646 people reported by systems filed under the county. Across Wyoming, the 775 active systems average 838 people each. Nationally, the average active community water system reports serving 6,703 people, so City of Mills is about 40% 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. Wyoming has 332 active community water systems, 43% of the state's 775 active systems. Groundwater under the influence of surface water is well or spring water that the regulator has found to be affected by nearby surface water, so it is regulated under the surface-water treatment rules. 24 Wyoming systems (3.1%) list groundwater under influence of surface water as their primary source.
Who owns and regulates City of Mills?
EPA lists City of Mills as owned by a local government. The WY state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 18 of the 48 active systems in Natrona County (38%) are also owned by a local government.
Does City of Mills have drinking water violations?
EPA's records list 8 violations for this system; 3 are health-based, and the most recent began in January 2025. The violations listed here began between July 1976 and January 2025. By type: 5 monitoring and reporting and 3 contaminant level above the legal limit. The contaminant or rule involved most often is Total trihalomethanes (TTHM) (3 of them). EPA lists 5 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 |
|---|---|---|---|---|
| 2025-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2024-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2024-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 1993-08-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | 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 |
| 1992-12-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1976-07-01 | Monitoring and reportingMonitoring, Regular · code 03 | Gross alpha (excluding radon and uranium)code 4000 | No | Archived |
| 1976-07-01 | Monitoring and reportingMonitoring, Regular · code 03 | Combined Radium (-226 and -228)code 4010 | No | Archived |
All 8 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 Mills: frequently asked questions
Who runs City of Mills?
City of Mills (PWSID WY5600036) is a community water system owned by a local government. It is regulated by the WY state drinking water program.
How many people does City of Mills serve?
City of Mills reports serving 4,050 people through 2,209 service connections in Natrona County, Wyoming.
Where does City of Mills get its water?
EPA SDWIS lists this system's primary water source as groundwater under influence of surface water. Groundwater under the influence of surface water is well or spring water that the regulator has found to be affected by nearby surface water, so it is regulated under the surface-water treatment rules.
Does City of Mills have any drinking water violations?
EPA's records list 8 violations for this system; 3 are health-based, and the most recent began in January 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 City of Mills' 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 8 violations for this system; 3 are health-based, and the most recent began in January 2025. For current results, consult the system's annual water quality report, EPA ECHO, or the WY state drinking water program.
Where can I find City of Mills' water quality report?
As a community water system, City of Mills 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 Natrona County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Casper, City of | Natrona | 59,000 | Community | Purchased surface water |
| Bar Nunn, Town of | Natrona | 4,000 | Community | Purchased surface water |
| Evansville, Town of | Natrona | 2,873 | Community | Surface water |
| Vista West Water Company | Natrona | 1,600 | Community | Purchased surface water |
| Pioneer Water & Sewer District | Natrona | 1,500 | Community | Purchased surface water |
| Alcova Lake Park Trailer Village | Natrona | 800 | 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, “Mills, City of, PWSID WY5600036, Wyoming”, https://aquacensus.com/water-systems/wyoming/mills-city-of-wy5600036 (data as of October 1, 2026).