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City of Chinook

What EPA’s and Montana’s records show in this utility’s water: nitrate, arsenic and other regulated chemicals; lead and copper; and violations since 2016, with the certification that handles each result.

Serves
1,300 people
Connections
807
Water source
Surface water
Based in
Chinook, MT
County
Blaine
Owner
Local government
The ZIP code it serves

59523

The short answer

1 result is above EPA’s legal limit. The worst: Haloacetic acids (HAA5), above the legal limit. 4 health-based violations since 2016.

What was found

Haloacetic acids (HAA5), total trihalomethanes (TTHM), nitrate, arsenic, chromium (total) and fluoride: Montana’s own results, samples taken from Feb. 10, 2020 to Oct. 6, 2026, with EPA’s 2012 to 2019 file for earlier years.

Uranium: EPA’s compliance monitoring file, samples taken from Aug. 8, 2017 to Aug. 8, 2017. Newer results are in the utility’s annual water quality report.

Above the legal limit1

Haloacetic acids (HAA5)

Forms or is added in treatment

Above the legal limit

72.8ppb

Highest yearly average, 2020 to 2026

2026 average: 41 ppb

Averaged by year, the highest was 72.8 ppb, in 2025, above EPA’s legal limit of 60 ppb. Its highest single sample was 121 ppb. In 2026, the latest year on file, its three samples averaged 41 ppb. EPA recorded a violation for haloacetic acids (HAA5) at this utility in 2025. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 49.5 ppb, in 2018.

What handles it

No certification claim covers this compound yet.

Below EPA’s limits2

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

70.6ppb

Highest yearly average, 2020 to 2026

2026 average: 60.8 ppb

Averaged by year, the highest was 70.6 ppb, in 2025, below EPA’s legal limit of 80 ppb. Its highest single sample was 98 ppb. In 2026, the latest year on file, its four samples averaged 60.8 ppb. EPA recorded no violation for total trihalomethanes (TTHM) at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 53.4 ppb, in 2016.

What handles it

  • NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
  • NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”

Nitrate

Comes from the source

Below EPA’s limits

0.16ppm

Highest sample; found in 5 of 7

2026: not found

The highest sample, in 2021, was 0.16 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, it wasn’t found in its one sample. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 0.14 ppm, in 2017.

What handles it

  • NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
  • NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
5 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Chromium (total)
  • Fluoride
  • Lead
  • Uranium

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
Total Haloacetic Acids (HAA5)The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageOct. 1, 2025 to Dec. 31, 20250.073 MG/LResolved
Total Haloacetic Acids (HAA5)The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJuly 1, 2025 to Sept. 30, 20250.077 MG/LResolved
Total Haloacetic Acids (HAA5)The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageApril 1, 2025 to June 30, 20250.079 MG/LResolved
Total Haloacetic Acids (HAA5)The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJan. 1, 2025 to March 31, 20250.071 MG/LResolved
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record.

What this report can’t tell you

  • Everything else. Haloacetic acids (HAA5), total trihalomethanes (TTHM), nitrate, arsenic, chromium (total) and fluoride results here are Montana’s own from 2020 on, with EPA’s national file for 2012 to 2019. Uranium comes from EPA’s file alone, which ends in 2019. City of Chinook’s own annual report, which it must send you every year, has newer results for those and the contaminants this page does not show.

  • Your own plumbing. Lead results are the 90th percentile across homes the utility samples. Your home’s service line, solder and fixtures decide yours. A certified lab test is the only way to know.

  • What it means for your health. This page reports what the records show and EPA’s limits and goals; it is not medical advice. If you are worried about a health effect, talk to a doctor or your local health department.

  • Anything after the latest data. SDWIS data is from 2026 Q3; UCMR 5 didn’t sample this utility; Montana’s results run from Feb. 10, 2020 to Oct. 6, 2026; EPA’s compliance samples are from Aug. 8, 2017 to Aug. 8, 2017.

Testing your own tap

City of Chinook’s results are for the water it sends out. What your own service line, solder and fixtures add shows up only in a test of your tap, by a lab Montana certifies.

No lab Montana certifies is within 75 miles of the area City of Chinook serves on the state’s list. Some take samples by mail; the state’s page lists them all.

Montana State Environmental Laboratory: Private well testing packages for bacteria, metals, nutrients, anions, organic chemicals and more, open to the public. Samples can be mailed, sent by the lab's free courier, or dropped off at the lab. Environmental Laboratory, Montana Department of Public Health and Human Services.

All 36 certified labs for Montana

Sources

PWSID MT0000174. Rebuilt from EPA data on Oct. 18, 2026.

Also in Blaine County

All Montana utilities

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