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Big Stone Colony Inc

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
130 people
Connections
15
Water source
Groundwater
Based in
Sand Coulee, MT
County
Cascade
Owner
Private

The short answer

2 results are above the health goal. The worst: Arsenic, above the health goal. No health-based violations on file since 2016.

What handles it

What was found

Arsenic, fluoride, nitrate, chromium (total) and total trihalomethanes (TTHM): Montana’s own results, samples taken from Feb. 27, 2020 to March 10, 2026, with EPA’s 2012 to 2019 file for earlier years.

Uranium: EPA’s compliance monitoring file, samples taken from March 15, 2017 to March 15, 2017. Newer results are in the utility’s annual water quality report.

Above the health goal2

Arsenic

Comes from the source

Above the health goal

2.0ppb

Highest yearly average, 2020 to 2025

2025, one sample: 2.0 ppb

Averaged by year, the highest was 2.0 ppb, in 2020: 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 2.0 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 2.0 ppb, in 2014.

What handles it

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

Uranium

Comes from the source

Above the health goal

2.0ppb

Highest yearly average, 2017

Averaged by year, the highest was 2.0 ppb, in 2017: 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 limits2

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.7ppm

Highest yearly average, 2021

Averaged by year, the highest was 0.7 ppm, in 2021, below EPA’s legal limit of 4.0 ppm. That is the only year on file.

What handles it

Nitrate

Comes from the source

Below EPA’s limits

0.4ppm

Highest sample; found in 7 of 7

2026, one sample: 0.4 ppm

The highest sample, in 2026, was 0.4 ppm, below EPA’s legal limit of 10 ppm. That was also the latest year on file, and its one sample was 0.4 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 0.43 ppm, in 2019.

What handles it

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

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

    Claim: Arsenic (Pentavalent)<=50 ppb Reduction

    For: Arsenic

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

  • NSF/ANSI 58

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

    For: Arsenic, Uranium

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

At the tap, or for the whole house?

These come with the water itself, so a whole-house system certified for the same claims treats every tap and shower. A filter at the tap treats drinking water for much less. 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

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Violations since 2016

No health-based violations on file with EPA since 2016. There are 2 monitoring or reporting violations: a sample missed, late or not reported.

What this report can’t tell you

  • Everything else. Arsenic, fluoride, nitrate, chromium (total) and total trihalomethanes (TTHM) 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. Big Stone Colony Inc’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. 27, 2020 to March 10, 2026; EPA’s compliance samples are from March 15, 2017 to March 15, 2017.

Testing your own tap

Big Stone Colony Inc’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 Big Stone Colony Inc 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 MT0003077. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Cascade County

All Montana utilities

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