Public water system · MT0042403

Active

Big Arm Flathead Lake Mt St Pk

At a glance

Big Arm Flathead Lake Mt St Pk (PWSID MT0042403) is an active transient non-community water system in Lake County, Montana. It reports serving 75 people through 20 service connections. Its primary water source is groundwater, and EPA lists it as owned by a state government. Of the 12 most recent violations in EPA's records, 3 are health-based, and the most recent began in August 2018.

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

Population served

Service connections

Primary source

Groundwater

System type

TNCWS

Transient non-community water system

System record

PWSIDMT0042403

System typeTransient non-community water system

Activity statusActive

Population served75

Service connections20

Primary water sourceGroundwater

Owner typeState government

Primacy agencyMT state drinking water program

City servedBig Arm

StateMontana

ZIP—

CountyLake County

How does Big Arm Flathead Lake Mt St Pk compare with other water systems in Lake County?

By EPA's size categories, Big Arm Flathead Lake Mt St Pk is a very small system (500 people or fewer). Lake County has 90 active public water systems. Its population served is about 66% below the county average of 220 people per system, and accounts for 0.4% of the 19,829 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 Big Arm Flathead Lake Mt St Pk is about half of 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. 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 Flathead Lake Mt St Pk?

EPA lists Big Arm Flathead Lake Mt St Pk as owned by a state government. 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. 8 of the 90 active systems in Lake County (8.9%) are also owned by a state government.

Does Big Arm Flathead Lake Mt St Pk have drinking water violations?

Of the 12 most recent violations in EPA's records, 3 are health-based, and the most recent began in August 2018. The violations listed here began between September 2014 and August 2018. By type: 9 monitoring and reporting and 3 required treatment not met. The contaminant or rule involved most often is Groundwater Rule (12 of them). EPA lists 12 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
2018-08-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2018-05-01	Required treatment not metTreatment Technique (SWTR and GWR) · code 41	Groundwater Rulecode 0700	Yes	Resolved
2018-05-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2017-08-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2017-07-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2017-05-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2016-09-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2016-07-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2016-05-01	Required treatment not metTreatment Technique (SWTR and GWR) · code 41	Groundwater Rulecode 0700	Yes	Resolved
2015-09-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved
2015-05-01	Required treatment not metTreatment Technique (SWTR and GWR) · code 41	Groundwater Rulecode 0700	Yes	Resolved
2014-09-01	Monitoring and reportingMonitoring of Treatment (SWTR-Unfilt/GWR) · code 31	Groundwater Rulecode 0700	No	Resolved

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.

Big Arm Flathead Lake Mt St Pk: frequently asked questions

Who runs Big Arm Flathead Lake Mt St Pk?

Big Arm Flathead Lake Mt St Pk (PWSID MT0042403) is a transient non-community water system owned by a state government. It is regulated by the MT state drinking water program.

How many people does Big Arm Flathead Lake Mt St Pk serve?

Big Arm Flathead Lake Mt St Pk reports serving 75 people through 20 service connections in Lake County, Montana.

Where does Big Arm Flathead Lake Mt St Pk 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 Flathead Lake Mt St Pk have any drinking water violations?

Of the 12 most recent violations in EPA's records, 3 are health-based, and the most recent began in August 2018. 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 Flathead Lake Mt St Pk'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, 3 are health-based, and the most recent began in August 2018. For current results, consult EPA ECHO, or the MT state drinking water program.

Where can I find Big Arm Flathead Lake Mt St Pk's water quality report?

The annual Consumer Confidence Report requirement applies to community water systems. Big Arm Flathead Lake Mt St Pk 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 Lake County

Water system	County	Population served	Type	Source
Polson City of	Lake	5,300	Community	Groundwater
Ronan City of	Lake	2,483	Community	Surface water
Pablo Lake County Water and Sewer Dist	Lake	2,175	Community	Groundwater
St Ignatius Town of	Lake	700	Community	Groundwater
Woods Bay Water and Sewer District	Lake	685	Community	Groundwater
Wilson Foods	Lake	600	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, “Big Arm Flathead Lake Mt St Pk, PWSID MT0042403, Montana”, https://aquacensus.com/water-systems/montana/big-arm-flathead-lake-mt-st-pk-mt0042403 (data as of October 1, 2026).