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Granite Park Water Association

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
250 people
Connections
120
Water source
Groundwater
Based in
Billings, MT
County
Yellowstone
Owner
Private
Hardness
Very hard
The ZIP code it serves

59106

The short answer

1 result is above EPA’s legal limit, and 1 more is above the health goal. The worst: Nitrate, above the legal limit. 1 health-based violation since 2016.

What handles it

What was found

Nitrate, uranium, total trihalomethanes (TTHM), fluoride, haloacetic acids (HAA5), arsenic and chromium (total): Montana’s own results, samples taken from March 19, 2020 to Sept. 10, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the legal limit1

Nitrate

Comes from the source

Above the legal limit

11.2ppm

Highest sample; found in 38 of 38

2026 average: 7.7 ppm

From 2023 to 2024, four samples were above EPA’s legal limit of 10 ppm, the highest 11.2 ppm in 2024. Two came back under the limit on the next sample at the same point and two have no follow-up sample on file within 30 days. In 2026, the latest year on file, its three samples averaged 7.7 ppm. EPA recorded a violation for nitrate at this utility in 2024. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 10.2 ppm, in 2014.

What handles it

  • NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
  • NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”

Above the health goal1

Uranium

Comes from the source

Above the health goal

15.9ppb

Highest yearly average, 2020 to 2024

2024, one sample: 15.8 ppb

Averaged by year, the highest was 15.9 ppb, in 2020: below EPA’s legal limit of 30 ppb, but above its health goal of zero. In 2024, the latest year on file, its one sample was 15.8 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 18 ppb, in 2014.

What handles it

Below EPA’s limits3

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

22ppb

Highest yearly average, 2020 to 2025

2025, one sample: 16 ppb

Averaged by year, the highest was 22 ppb, in 2022, below EPA’s legal limit of 80 ppb. In 2025, the latest year on file, its one sample was 16 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 21 ppb, in 2018.

What handles it

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

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.5ppm

Highest yearly average, 2020 to 2024

2024, 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 2024, 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 0.5 ppm, in 2014.

What handles it

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

5.7ppb

Highest yearly average, 2022 to 2025

2025, one sample: 4.4 ppb

Averaged by year, the highest was 5.7 ppb, in 2022, below EPA’s legal limit of 60 ppb. In 2025, the latest year on file, its one sample was 4.4 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 7.0 ppb, in 2015.

What handles it

No certification claim covers this compound yet.

3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Chromium (total)
  • Lead

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: Nitrate/Nitrite (30 ppm challenge)

    For: Nitrate

  • NSF/ANSI 58

    Claims: Nitrate/Nitrite Reduction, Uranium

    For: Nitrate, Uranium

    Other certifiers’ wording: Nitrate

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

The best reverse osmosis systems, ranked

Hardness

Very hard, 1060 mg/L (62 grains per gallon), at its one sampling point, in 2025.

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 62 grains per gallon, salt includedSoftener or salt-free conditioner?Montana water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
Nitrate-NitriteA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2024 to March 31, 202410.8 MG/LArchived
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. Nitrate, uranium, total trihalomethanes (TTHM), fluoride, haloacetic acids (HAA5), arsenic and chromium (total) results here are Montana’s own from 2020 on, with EPA’s national file for 2012 to 2019. Granite Park Water Association’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 19, 2020 to Sept. 10, 2026.

Testing your own tap

Granite Park Water Association’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.

The lab Montana certifies closest to the area Granite Park Water Association serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Energy Laboratories, Inc.

    Billings, MT · about 8 miles

    Certified for bacteria, minerals and other inorganics, organic chemicals

    (800) 735-4489

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 MT0004563. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Yellowstone County

All Montana utilities

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