waterbycounty
EPA SDWIS

Petroleum County Water Quality

Petroleum County, Montana

Water Grade

A

Water Score

86.0

Violations

0

State Rank

#13

of 55 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

A

Based on EPA compliance history and violation data

Water Score

86/100

Higher = better quality

Health Violations

0

Health-based violations

Violation Rate

0.0%

Systems with violations

Water Advisory: Petroleum County

Water Verdict

Petroleum County receives an excellent water quality assessment with a grade of A and a score of 86.0 out of 100. The water supply meets or exceeds federal safety standards, and residents can generally drink tap water with confidence.

Violation Context

Petroleum County has recorded zero health-based violations, indicating that the water system has met all federal safety standards during the reporting period. The violation rate is zero per 1,000 residents, which is the best possible outcome.

Consumer Guidance

Tap water in Petroleum County is generally safe to drink based on available data. Residents should still review their utility's annual Consumer Confidence Report for transparency on detected contaminants. 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

Petroleum County has better water quality than the average county in Montana. Its water score is 37.1 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

0.0%

0 of 14 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

6

Active in the past 5 years

Measurements Recorded

137

137 total readings

Most Measured

  • Physical
  • Biological, Algae, Phytoplankton
  • Cyanotoxins, Phytotoxins

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

13.4cfs

May 14, 6:45 PM UTC

vs Long-Term Average

5%

Well below typical

Primary Streamgage

Musselshell River at Mosby MT

USGS site
06130500
Drainage area
7,784 sq mi
Long-term mean
293 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 Petroleum County, Montana?
Petroleum County, Montana has a drinking-water quality grade of A with a score of 86.0/100, based on EPA SDWIS compliance data. The county has 0 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 Petroleum County?
Petroleum County has 0 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). Zero violations is an excellent record indicating consistent compliance with federal drinking water standards.
How healthy are the watersheds in Petroleum County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 0.0% of Petroleum County's 14 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 Petroleum County?
EPA's Water Quality Portal records 137 measurements from 6 monitoring sites in Petroleum County over the past five years. The most frequently measured characteristic groups are Physical, Biological, Algae, Phytoplankton, Cyanotoxins, Phytotoxins. 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 Petroleum County right now?
Petroleum County's primary USGS streamgage on the Musselshell River is currently reading 13.4 cubic feet per second — 5% of the long-term mean of 292.74 cfs. This is well below typical — often a signal of drought stress on source water. For genuine real-time data, visit waterdata.usgs.gov.
How does Petroleum County water compare to the Montana average?
Petroleum County's SDWIS water quality score of 86.0/100 is higher 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 Petroleum County?
Based on EPA SDWIS data, Petroleum County has a water quality grade of A (86.0/100). This indicates good to excellent water quality with strong SDWIS compliance. 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).
Does Petroleum County have clean drinking water?
Petroleum County has 0 health-based drinking water violations according to EPA records. With a water quality score of 86.0/100 and grade A, the county's drinking water meets EPA standards with no recorded health violations. Note: drinking-water compliance speaks to the public water system, not necessarily to the watershed itself — check the Watershed Health zone for ATTAINS §303(d) data.
How does Petroleum County rank for water quality in Montana?
Petroleum County ranks #13 out of 55 counties in Montana by SDWIS water quality score (1 = best). With a score of 86.0/100, it falls in the top 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

Big Horn County

Montana

A

86.0

Water score

Broadwater County

Montana

A

86.0

Water score

Carter County

Montana

A

86.0

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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