Public water system · MT0002008
ActiveHardin Koa Cistern
At a glance
Hardin Koa Cistern (PWSID MT0002008) is an active transient non-community water system in Big Horn County, Montana. It reports serving 100 people through 49 service connections. Its primary water source is purchased surface water, and EPA lists it as privately owned. Of the 12 most recent violations in EPA's records, 2 are health-based, and the most recent began in January 2026.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
100
Service connections
49
Primary source
SWP
Purchased surface water
System type
TNCWS
Transient non-community water system
System record
How does Hardin Koa Cistern compare with other water systems in Big Horn County?
By EPA's size categories, Hardin Koa Cistern is a very small system (500 people or fewer). Big Horn County has 23 active public water systems. Its population served is well below the county average of 449 people per system, and accounts for 1% of the 10,335 people reported by systems filed under the county. Across Montana, the 2,378 active systems average 489 people each. Nationally, the average active transient non-community water system reports serving 144 people, so Hardin Koa Cistern is about 31% below that figure.
What does “transient non-community water system” mean?
A transient non-community water system serves places where people do not stay long, such as gas stations and campgrounds, and regularly serves at least 25 people a day for at least 60 days a year. Montana has 1,206 active transient non-community water systems, 51% of the state's 2,378 active systems. Purchased surface water means the system buys surface water from another public water system rather than drawing its own. 212 Montana systems (8.9%) list purchased surface water as their primary source.
Who owns and regulates Hardin Koa Cistern?
EPA lists Hardin Koa Cistern as privately owned. The MT 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 23 active systems in Big Horn County (48%) are also privately owned.
Does Hardin Koa Cistern have drinking water violations?
Of the 12 most recent violations in EPA's records, 2 are health-based, and the most recent began in January 2026. The violations listed here began between October 1982 and January 2026. By type: 5 monitoring, 5 monitoring and reporting, 1 required treatment not met and 1 contaminant level above the legal limit. The contaminant or rule involved most often is Revised Total Coliform Rule (6 of them). EPA lists 6 as archived, 5 as resolved and 1 as addressed. 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. Addressed means the violation is not resolved or archived and is covered by formal enforcement.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2026-01-17 | Required treatment not metTreatment Technique, Level 1 Assessment (RTCR) · code 2A | Revised Total Coliform Rulecode 8000 | Yes | Addressed |
| 2025-10-01 | MonitoringMonitoring, Routine (RTCR) · code 3A | Revised Total Coliform Rulecode 8000 | No | Archived |
| 2024-09-01 | MonitoringMonitoring, Routine (RTCR) · code 3A | Revised Total Coliform Rulecode 8000 | No | Archived |
| 2024-07-01 | MonitoringMonitoring, Routine (RTCR) · code 3A | Revised Total Coliform Rulecode 8000 | No | Archived |
| 2024-02-01 | MonitoringMonitoring, Routine (RTCR) · code 3A | Revised Total Coliform Rulecode 8000 | No | Archived |
| 2017-04-01 | MonitoringMonitoring, Routine (RTCR) · code 3A | Revised Total Coliform Rulecode 8000 | No | Resolved |
| 2006-10-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 2006-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2006-06-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1994-06-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1983-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Archived |
| 1982-10-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | 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.
Hardin Koa Cistern: frequently asked questions
Who runs Hardin Koa Cistern?
Hardin Koa Cistern (PWSID MT0002008) is a transient non-community water system privately owned. It is regulated by the MT state drinking water program.
How many people does Hardin Koa Cistern serve?
Hardin Koa Cistern reports serving 100 people through 49 service connections in Big Horn County, Montana.
Where does Hardin Koa Cistern get its water?
EPA SDWIS lists this system's primary water source as purchased surface water. Purchased surface water means the system buys surface water from another public water system rather than drawing its own.
Does Hardin Koa Cistern have any drinking water violations?
Of the 12 most recent violations in EPA's records, 2 are health-based, and the most recent began in January 2026. 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 Hardin Koa Cistern'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, 2 are health-based, and the most recent began in January 2026. For current results, consult EPA ECHO, or the MT state drinking water program.
Where can I find Hardin Koa Cistern's water quality report?
The annual Consumer Confidence Report requirement applies to community water systems. Hardin Koa Cistern is a transient non-community water system, so it is not required to publish one; like every public water system, it must notify the people it serves about violations under EPA's public notification rules.
Other water systems in Big Horn County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Hardin City of | Big Horn | 3,500 | Community | Surface water |
| Little Bighorn Battlefield Nm | Big Horn | 2,020 | Non-transient non-community | Groundwater |
| Hardin Eastbound Rest Area | Big Horn | 877 | Transient non-community | Groundwater |
| Hardin Westbound Rest Area | Big Horn | 715 | Transient non-community | Groundwater |
| Lodge Grass Town of | Big Horn | 480 | Community | Groundwater |
| Fort Smith Water and Sewer District | Big Horn | 450 | 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, “Hardin Koa Cistern, PWSID MT0002008, Montana”, https://aquacensus.com/water-systems/montana/hardin-koa-cistern-mt0002008 (data as of October 1, 2026).