Public water system · 083090309
ActiveBig Arm Water System
At a glance
Big Arm Water System (PWSID 083090309) is an active community water system in Montana. It reports serving 116 people through 23 service connections. Its primary water source is groundwater, and EPA lists it as Native American-owned. EPA's records list 7 violations for this system; 1 is health-based, and the most recent began in October 2023.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
116
Service connections
23
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does Big Arm Water System compare with other water systems in Montana?
By EPA's size categories, Big Arm Water System is a very small system (500 people or fewer). Across Montana, the 2,378 active systems average 489 people each. Nationally, the average active community water system reports serving 6,703 people, so Big Arm Water System 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. Montana has 853 active community water systems, 36% of the state's 2,378 active systems. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 1,994 Montana systems (84%) list groundwater as their primary source.
Who owns and regulates Big Arm Water System?
EPA lists Big Arm Water System as Native American-owned. The EPA Region 08 is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act.
Does Big Arm Water System have drinking water violations?
EPA's records list 7 violations for this system; 1 is health-based, and the most recent began in October 2023. The violations listed here began between April 2017 and October 2023. By type: 6 monitoring and reporting and 1 required treatment not met. The contaminants or rules involved are Lead and Copper Rule, Groundwater Rule, Combined Uranium and Combined Radium (-226 and -228). EPA lists 7 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 |
|---|---|---|---|---|
| 2023-10-01 | Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52 | Lead and Copper Rulecode 5000 | No | Resolved |
| 2017-11-24 | Required treatment not metFailure To Address Deficiency · code 45 | Groundwater Rulecode 0700 | Yes | Resolved |
| 2017-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Combined Uraniumcode 4006 | No | Resolved |
| 2017-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Combined Radium (-226 and -228)code 4010 | No | Resolved |
| 2017-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Radium-226code 4020 | No | Resolved |
| 2017-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Gross alpha (excluding radon and uranium)code 4000 | No | Resolved |
| 2017-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Radium-228code 4030 | No | Resolved |
All 7 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.
Big Arm Water System: frequently asked questions
Who runs Big Arm Water System?
Big Arm Water System (PWSID 083090309) is a community water system Native American-owned. It is regulated by the EPA Region 08.
How many people does Big Arm Water System serve?
Big Arm Water System reports serving 116 people through 23 service connections in Montana.
Where does Big Arm Water System 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 Big Arm Water System have any drinking water violations?
EPA's records list 7 violations for this system; 1 is health-based, and the most recent began in October 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 Big Arm Water System'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 7 violations for this system; 1 is health-based, and the most recent began in October 2023. For current results, consult the system's annual water quality report, EPA ECHO, or the EPA Region 08.
Where can I find Big Arm Water System's water quality report?
As a community water system, Big Arm Water System 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 Montana
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Billings City of | Yellowstone | 114,000 | Community | Surface water |
| Missoula Water | Missoula | 68,200 | Community | Groundwater |
| Great Falls City of | Cascade | 60,000 | Community | Surface water |
| Bozeman City of | Gallatin | 56,000 | Community | Surface water |
| Butte Silverbow Water Dept | Silver Bow | 33,000 | Community | Surface water |
| Helena Water System | Lewis and Clark | 32,091 | Community | Surface water |
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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, “Big Arm Water System, PWSID 083090309, Montana”, https://aquacensus.com/water-systems/montana/big-arm-water-system-083090309 (data as of October 1, 2026).