waterbycounty
EPA SDWIS

Missoula County Water Quality

Missoula County, Montana

Water Grade

F

Water Score

40.6

Violations

27

State Rank

#29

of 55 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

F

Based on EPA compliance history and violation data

Water Score

40.6/100

Higher = better quality

Health Violations

27

Health-based violations

Violation Rate

31.4%

Systems with violations

Water Advisory: Missoula County

Water Verdict

Missoula County receives a below-average water quality assessment with a grade of F and a score of 40.6 out of 100. Residents should review their utility's Consumer Confidence Report and may want to consider additional water filtration for drinking.

Violation Context

Missoula County has recorded 27 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 31.4 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Residents of Missoula County are advised to use filtered or bottled water for drinking and cooking until water quality improves. A reverse-osmosis or activated-carbon filter certified to remove the contaminants listed in the utility's Consumer Confidence Report is recommended. With 27 recorded health violations, staying informed about utility communications and boil-water notices is especially important. For long-term peace of mind, request your utility's latest Consumer Confidence Report and consider independent water testing if you have specific health concerns.

Regional Context

Missoula County has poorer water quality than the average county in Montana. Its water score is 8.3 points lower than the state average, suggesting more challenges with contamination control or infrastructure than neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

0.0%

0 of 70 assessed

Mostly healthy

Top Impairment Causes

No specific impairment causes reported for this county's assessed water bodies.

Source: EPA ATTAINS · Reporting cycle 2022

Impairment is determined under the Clean Water Act §303(d): a water body is impaired when it fails to meet state-defined quality standards for designated uses (drinking, recreation, aquatic life). Assessment coverage varies by state — counties without assessed water bodies are not shown.

Past 5 years

Water Quality Monitoring

Monitoring Sites

155

Active in the past 5 years

Measurements Recorded

15K

15,023 total readings

Most Measured

  • Physical
  • Nutrient
  • Inorganics, Minor, Metals

Categories measured most frequently

Data from the EPA Water Quality Portal (WQP), aggregating monitoring records from federal, state, and tribal sources. Each measurement represents a single sample analyzed for a specific characteristic (e.g., E. coli, pH, dissolved oxygen, nitrogen).

Live USGS Streamgage

River & Stream Conditions

Current Discharge

19.7Kcfs

May 14, 6:00 PM UTC

vs Long-Term Average

369%

Well above typical

Primary Streamgage

Clark Fork below Missoula MT

USGS site
12353000
Drainage area
9,017 sq mi
Long-term mean
5,345 cfs

One representative streamgage (the one with the largest drainage area in the county). Many counties have multiple gauges — this view summarizes the primary one. The long-term mean is the full-record annual average; "% of typical" compares the latest reading against that average.

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Frequently Asked Questions

What is the water quality in Missoula County, Montana?
Missoula County, Montana has a drinking-water quality grade of F with a score of 40.6/100, based on EPA SDWIS compliance data. The county has 27 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in Missoula County?
Missoula County has 27 health-based drinking water violations recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Violations may have been resolved — check with your local water utility for current status.
How healthy are the watersheds in Missoula County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 0.0% of Missoula County's 70 assessed water bodies are classified as impaired (0 impaired). Impairment means the water body fails to meet state quality standards for at least one designated use — drinking water source, recreation, aquatic life, or fish consumption. Note: watershed impairment doesn't always translate to tap-water issues; treatment plants can remove most regulated contaminants.
How much water-quality monitoring happens in Missoula County?
EPA's Water Quality Portal records 15,023 measurements from 155 monitoring sites in Missoula County over the past five years. The most frequently measured characteristic groups are Physical, Nutrient, Inorganics, Minor, Metals. Each measurement is a single sample analyzed for one characteristic (E. coli, pH, dissolved oxygen, etc.). High monitoring density means more scientific evidence behind any reported signal — it does not by itself indicate water quality.
What's happening with rivers in Missoula County right now?
Missoula County's primary USGS streamgage on the Clark Fork below Missoula MT is currently reading 19,700 cubic feet per second — 369% of the long-term mean of 5,344.73 cfs. This is well above typical — often a signal of recent precipitation or storm runoff. For genuine real-time data, visit waterdata.usgs.gov.
How does Missoula County water compare to the Montana average?
Missoula County's SDWIS water quality score of 40.6/100 is lower than the Montana state average of 48.9. The average water quality grade across Montana is D, based on data from 55 counties with available SDWIS data.
Is tap water safe to drink in Missoula County?
Based on EPA SDWIS data, Missoula County has a water quality grade of F (40.6/100). This indicates below-average compliance with significant violations. Residents may want to consider home water filtration or independent testing. The grade speaks to the public water system, not the watershed — for watershed-level concerns, see the Watershed Health zone. For the most up-to-date information, contact your local water utility or review your Consumer Confidence Report (CCR).
Why does Missoula County have so many water violations?
Missoula County has 27 health-based drinking water violations on record from the EPA SDWIS database. A higher violation count can result from aging infrastructure, underfunded water utilities, agricultural runoff contamination, or industrial pollution. Counties with more water systems may also see more violations simply due to scale. Residents concerned about water quality should consider independent water testing and home filtration systems.
How does Missoula County rank for water quality in Montana?
Missoula County ranks #29 out of 55 counties in Montana by SDWIS water quality score (1 = best). With a score of 40.6/100, it falls in the middle third of counties statewide. The ranking reflects EPA SDWIS compliance only — not watershed impairment, monitoring density, or streamflow, which are tracked separately on this page.

Counties with Similar Water Quality

Yellowstone County

Montana

D

42.1

Water score

Phillips County

Montana

F

36.7

Water score

Teton County

Montana

F

33.5

Water score

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.

Watershed health and impaired-waterway data from the EPA ATTAINS Clean Water Act §303(d) assessments — state-reported, EPA-finalized.

Water-quality monitoring counts from the EPA Water Quality Portal (WQP) — federated USGS, EPA, and state agency sampling records over a rolling 5-year window.

Live streamflow from the USGS National Water Information System (NWIS) — continuous discharge measurements from the largest-drainage gauge in each county, compared against the full-record long-term annual mean.

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.

By Logan Johnson, Founder & Data EditorUpdated Reviewed by Logan Johnson, Founder & Data Editor

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