waterbycounty
Compiled federal source snapshot

Montana Water Quality

Drinking water data for all 51 counties.

Avg SDWIS Compliance Index

49.2

Most Common Five-Year SDWIS Compliance Band

A

Counties with Data

51

of 51 total

County water atlas

Montana water signals by county

A state-level 2.5D view across drinking-water compliance, watershed impairment, monitoring density, and streamflow snapshot context. Pin any county, switch layers, then use the lens controls to compare index ranges, recorded violation rates, or impaired watersheds without leaving the page.

Counties

51

Avg SDWIS index

49.2

Watersheds

0

ATTAINS counties

Monitoring

51

43 fresh USGS snapshots

State atlas layers combine EPA SDWIS health-based violations, EPA ATTAINS 303(d) impairment assessments, EPA Water Quality Portal monitoring sites, and representative USGS NWIS streamflow gauges. Streamflow values appear only for fresh pipeline snapshots, not as a continuously updated stream. County pages include the observation time and year.

Prepared by ByCounty Editorial TeamPublished by WaterByCounty

Multi-source coverage in Montana

Beyond Drinking Water

EPA SDWIS

51/ 51

counties with drinking-water compliance data

297 health violations statewide (5yr)

EPA ATTAINS

—

No §303(d) assessments yet for Montana

EPA WQP

2,975

monitoring sites across 51 counties

481,278 total readings (5yr window)

USGS NWIS

43

counties with a fresh pipeline snapshot

3 above40 below

State atlas notes

What stands out in Montana

County water quality is not one number. The strongest read comes from comparing drinking-water compliance against watershed impairment, monitoring density, and streamflow context. Use these signals as a starting point, then open any county profile for source-level detail.

Compliance spread

Big Horn County has the highest value in the published state SDWIS Compliance Index table at 86.2/100, while Treasure County has the lowest at 0.2/100. That is a 86.0 point gap inside one state.

Zero health violations

20

3+ health violations

19

Monitoring hubs

Rosebud County841 sitesGallatin County217 sitesLincoln County172 sites

Lowest flow reads

Sheridan County1%Daniels County2%Powder River County3%

Highest fresh streamflow pipeline snapshots: Hill County (282%, observation 2026), Pondera County (167%, observation 2026), Blaine County (152%, observation 2026). These are source-data observations, not household tap-water conclusions.

All Montana Counties

CountySDWIS Compliance Index
Big Horn County86.2
Broadwater County86.2
Daniels County86.2
Deer Lodge County86.2
Fallon County86.2
Garfield County86.2
Glacier County86.2
Judith Basin County86.2
Meagher County86.2
Musselshell County86.2
Petroleum County86.2
Powder River County86.2
Powell County86.2
Roosevelt County86.2
Sanders County86.2
Sheridan County86.2
Silver Bow County86.2
Stillwater County86.2
Sweet Grass County86.2
Wheatland County86.2
Cascade County55.7
Gallatin County53.8
Flathead County50.5
Yellowstone County46.0
Missoula County45.6
Toole County42.9
Hill County42.4
Ravalli County40.9
Park County39.1
Lake County37.5
Teton County34.3
Beaverhead County28.4
Lewis and Clark County28.4
Valley County27.9
Phillips County25.9
Carbon County25.8
Mineral County25.0
Pondera County25.0
Lincoln County24.6
Madison County22.5
Custer County14.8
Chouteau County14.4
Dawson County11.4
Richland County8.5
Rosebud County6.2
Jefferson County4.3
Golden Valley County2.7
Fergus County1.1
Blaine County0.8
Granite County0.7
Treasure County0.2

Frequently Asked Questions

Which Montana county has the highest SDWIS Compliance Index?
Big Horn County has the highest SDWIS Compliance Index in the published Montana cohort at 86.2/100. This WaterByCounty relative comparison is not an EPA score and does not establish current conditions for a utility or address.
What does the Five-Year SDWIS Compliance Band mean?
The band is derived only from each county aggregation's recorded health-violation rate per 100,000 people served for the stated five-year source window. It is separate from the relative SDWIS Compliance Index and is not a current determination for a specific utility or address.
Which USGS streamflow records are shown across Montana?
WaterByCounty has 43 fresh USGS pipeline snapshots in the published Montana cohort. Each county page shows its observation timestamp and year. A pipeline snapshot is not a continuously updated reading or a tap-water safety measure.
Where can Montana residents find current official information?
Review the applicable utility's Consumer Confidence Report, active notices, and the state drinking-water agency. WaterByCounty's county-level historical aggregations do not establish the current status of a specific utility, address, private well, or household plumbing system.
What does Water Quality Portal monitoring volume show in Montana?
The published county records contain 481,278 results from 2,975 monitoring locations in the site's five-year aggregation. Monitoring volume does not by itself indicate better or worse water quality.

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. The WaterByCounty SDWIS Compliance Index reflects the recorded rate and is not an EPA score.

Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.

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