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City of Colstrip

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
2,350 people
Connections
913
Water source
Surface water
Based in
Colstrip, MT
County
Rosebud
Owner
Local government
Hardness
Very hard
The ZIP code it serves

59323

The short answer

1 result is above EPA’s legal limit, and 3 more are above the health goal. The worst: Total trihalomethanes (TTHM), above the legal limit. 2 health-based violations since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 1998 to 2025.

Total trihalomethanes (TTHM), arsenic, uranium, haloacetic acids (HAA5), fluoride, nitrate and chromium (total): Montana’s own results, samples taken from March 9, 2020 to Sept. 15, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the legal limit1

Total trihalomethanes (TTHM)

Forms or is added in treatment

Above the legal limit

72ppb

Highest yearly average, 2020 to 2026

2026 average: 39.7 ppb

Averaged by year, the highest was 72 ppb, in 2024, below EPA’s legal limit of 80 ppb. Its highest single sample was 105 ppb. In 2026, the latest year on file, its three samples averaged 39.7 ppb. EPA judges this limit at each sampling point, and recorded a violation for total trihalomethanes (TTHM) at this utility in 2024. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 76.8 ppb, in 2013.

What handles it

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

Above the health goal3

Arsenic

Comes from the source

Above the health goal

3.0ppb

Highest yearly average, 2020 to 2025

2025, one sample: 1.0 ppb

Averaged by year, the highest was 3.0 ppb, in 2024: below EPA’s legal limit of 10 ppb, but above its health goal of zero. In 2025, the latest year on file, its one sample was 1.0 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 3.0 ppb, in 2012.

What handles it

  • NSF/ANSI 58 look for “Arsenic (Pentavalent)<=50 ppb Reduction”
  • NSF/ANSI 53 look for “Arsenic (Pentavalent)<=50 ppb Reduction”

Lead

Comes from pipes, often your own

Above the health goal

1.0ppb

90th percentile, 2023 to 2025

In the latest period, 9 in 10 homes sampled were at or below 1.0 ppb, below EPA’s action level of 15 ppb. The action level drops to 10 ppb on Nov. 1, 2027. EPA’s health goal for lead is zero.

What handles it

Uranium

Comes from the source

Above the health goal

0.9ppb

Highest yearly average, 2022

Averaged by year, the highest was 0.9 ppb, in 2022: below EPA’s legal limit of 30 ppb, but above its health goal of zero. That is the only year on file.

What handles it

Below EPA’s limits3

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

41.2ppb

Highest yearly average, 2020 to 2026

2026 average: 25 ppb

Averaged by year, the highest was 41.2 ppb, in 2024, below EPA’s legal limit of 60 ppb. Its highest single sample was 54 ppb. In 2026, the latest year on file, its three samples averaged 25 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 46.8 ppb, in 2017.

What handles it

No certification claim covers this compound yet.

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.5ppm

Highest yearly average, 2020 to 2025

2025, one sample: 0.4 ppm

Averaged by year, the highest was 0.5 ppm, in 2020, below EPA’s legal limit of 4.0 ppm. In 2025, the latest year on file, its one sample was 0.4 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.9 ppm, in 2012.

What handles it

Nitrate

Comes from the source

Below EPA’s limits

0.14ppm

Highest sample; found in 6 of 6

2025, one sample: 0.08 ppm

The highest sample, in 2021, was 0.14 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, its one sample was 0.08 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 0.15 ppm, in 2017.

What handles it

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

What handles it

A certification covers specific claims, not a whole standard. Look for these claims on the certifier’s listing, not the box. Wording varies a little: NSF writes “Lead Reduction,” WQA just “Lead.”

  • NSF/ANSI 53

    Claims: Trihalomethanes (TTHM) Reduction, Arsenic (Pentavalent)<=50 ppb Reduction, Lead Reduction

    For: Total trihalomethanes (TTHM), Arsenic, Lead

    Other certifiers’ wording: VOC Reduction; Arsenic (III) (50 ppb influent level)

  • NSF/ANSI 58

    Claims: Trihalomethanes (TTHM) Reduction, Arsenic (Pentavalent)<=50 ppb Reduction, Lead Reduction, Uranium

    For: Total trihalomethanes (TTHM), Arsenic, Lead, Uranium

    Other certifiers’ wording: Arsenic (Pentavalent)<=300 ppb Reduction; Arsenic (V) (300 ppb influent level)

At the tap, or for the whole house?

Lead and copper usually come from pipes and fixtures inside or near your home. A whole-house system sits where water enters, so it cannot catch what your own plumbing adds after it. For those, the filter that counts is the one at the tap. How whole-house systems compare.

Filters with those claims on a certifier’s listing

Disclosure: TapBuff earns a commission if you buy through some links on this page. It does not change which standard or filter we name. As an Amazon Associate, TapBuff earns from qualifying purchases. How TapBuff makes money

Compare five-year costs

The best reverse osmosis systems, ranked

The best water filters for lead, ranked

Hardness

Very hard, 191 mg/L (11.1 grains per gallon), at its one sampling point, 2016 to 2021.

Hardness is calcium and magnesium. EPA sets no limit for it: it shows up as scale on fixtures and in water heaters, and as soap that won’t lather. USGS calls water above 60 mg/L moderately hard, above 120 hard and above 180 very hard.

Softeners compared at 11.1 grains per gallon, salt includedSoftener or salt-free conditioner?Montana water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJuly 1, 2024 to Sept. 30, 202481 UG/LResolved
Surface Water Treatment RuleRequired treatment for surface water or groundwater was not met.EPA: Treatment Technique (SWTR and GWR)July 1, 2024 to July 31, 2024—Resolved
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 6 monitoring or reporting violations not shown.

What this report can’t tell you

  • Everything else. Total trihalomethanes (TTHM), arsenic, uranium, haloacetic acids (HAA5), fluoride, nitrate and chromium (total) results here are Montana’s own from 2020 on, with EPA’s national file for 2012 to 2019. City of Colstrip’s own annual report, which it must send you every year, has 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 March 9, 2020 to Sept. 15, 2026.

Testing your own tap

City of Colstrip’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 Colstrip 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 MT0000180. Rebuilt from EPA data on Oct. 18, 2026.

Nearby

All Montana utilities

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