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Montana water profile

Nitrate in Montana community water systems

Montana's nitrate gathers in its irrigated and fast-growing valleys: the Yellowstone around Billings, the Helena valley, and the Gallatin around Bozeman. See where the pattern concentrates and what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 766 Montana systems →

Search by the utility or system name shown on a water bill. Example: City of Billings. Private wells are not in this inventory.

96%
of the state’s 798 active community water systems have a current result here
766
systems with a current nitrate result
772,307
people served by those reporting systems
2.7%
of reporting systems at or above 5 mg/L
How to read these numbers Each system is placed into a band by its most recent reported result within a rolling three-year window. The bands describe how strongly human activity, read from nitrate, has marked a water source; they are not a safety verdict. Figures describe system reporting, not nitrate measured at an individual tap.

How Montana's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
531 systems · 525,896 served
Human impact likely
1.00–2.99 mg/L as N
165 systems · 220,638 served
Human impact clear
3.00–4.99 mg/L as N
49 systems · 21,115 served
Health-study range
5.00–9.99 mg/L as N
20 systems · 4,602 served
Above the federal limit
10.00 mg/L and above
1 system · 56 served

Each system appears in one band only, placed by its most recent reported result in the current three-year window. Counts sit beside people served so a small number of larger systems cannot hide behind a row of tiny ones. Of the 21 systems reporting 5 mg/L or more, 8 stayed at or above 5 across the whole three-year range; the other 13 reached it only on a high sample and otherwise ran lower.

Most recent reading Jul 2026; the typical system was last tested around Dec 2025. 684 systems sampled their own water; 82 systems carry a supplier’s result.

The named systems

Every reading here belongs to a utility with a name

Highest recent readings
SystemMost recent resultBandBased onPeople served
King Ranch Colony11.50 mg/LJun 2026Above the federal limit12 samples56
Duck Creek Mobile Home Park8.58 mg/LJun 2026a high point — runs lowerHealth-study range30 samples70
Crystal Springs Water System8.31 mg/LApr 2026Health-study range12 samples225
Turner Colony8.18 mg/LJun 2026a high point — runs lowerHealth-study range12 samples50
Granite Park Water Association7.59 mg/LApr 2026Health-study range14 samples250
Skycrest Estates Subdivision7.31 mg/LMar 2026Health-study range6 samples235
Mobile City Home Park No 27.08 mg/LFeb 2025Health-study range10 samples300
Blue Grass Water Users Association7.03 mg/LJun 2026Health-study range12 samples60
Largest systems
SystemMost recent resultBandBased onPeople served
Billings City Of0.37 mg/LMar 2026Natural background2 samples114,000
Missoula Water1.00 mg/LJun 2026Human impact likely22 samples68,200
Great Falls City Of0.05 mg/LJul 2024Natural background*1 sample60,000
Bozeman City Of0.17 mg/LJun 2026Natural background3 samples56,000
Butte Silverbow Water Dept0.02 mg/LNov 2025Natural background8 samples33,000

Each result shows its date and what it rests on, so a lone sample is never taken for a settled measurement. A single high sample is not a complete account of what a household drinks.

Where higher nitrate concentrates

Higher results follow the irrigated and growing valleys

Human impact is clear on drinking water served in 16 of Montana’s 56 counties. Each is shaded by how many of its systems reported 3.00 mg/L as N or above. Shading counts systems, not severity — a county with many small utilities can outrank one holding a single larger system that reads higher. The table beside the map splits the two bands so that difference stays visible.

MT counties shaded by number of community water systems reporting nitrate at or above 3.00 mg/L as NCounties are shaded by how many community water systems reported nitrate at or above 3.00 mg/L as N in the three years from August 9, 2023 to August 9, 2026. The same counts appear in the table below this map.Lewis and Clark County — 11 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveRavalli County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveFlathead County — 6 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveRichland County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveYellowstone County — 5 systems at 3.00–4.99 mg/L as N; 10 systems at 5.00 mg/L as N or aboveGallatin County — 10 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveJefferson County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveTeton County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveFergus County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMcCone County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLake County — 5 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMissoula County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePark County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveBlaine County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveCarbon County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveCascade County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or above
none1–23–56–1112–2526+Number of drinking water systems reporting ≥3.00 mg/L NO₃–N per county as of August 9, 2026

Yellowstone leads this layer with 10 reporting systems, followed by Lewis and Clark, Park, Blaine. Higher results follow the irrigated and growing valleys.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Yellowstone51015
Lewis and Clark11314
Gallatin10010
Flathead617
Lake505

Counts use each system's most recent reported result in the current three-year window. A system appears in only one of the two bands.

Find a specific Montana system

What the statewide pattern says

Irrigation recharge and subdivision septic

Montana's higher nitrate is a valley story: flood-irrigation recharge in the Yellowstone valley, septic-driven growth in the Gallatin and Helena valleys — with a natural rock-weathering source in the mix.

The Yellowstone valley is the state's best-measured case. The Montana Bureau of Mines and Geology sampled 119 alluvial wells between Billings and Forsyth: 53 percent ran above 2 mg/L — its threshold for land-use impact — 14 wells exceeded the 10 mg/L federal limit, and the maximum was 209 mg/L. Elevated nitrate sat beneath unsewered Billings subdivisions on former farmland and beside irrigated sugar-beet fields and a feedlot in Treasure County (MBMG, Middle Yellowstone Groundwater Assessment). Flood-irrigation recharge dominates the aquifer, so what is spread on fields reaches the water table.

In the upper Gallatin, the Bureau's side-by-side sampling shows development doing the work: every well on the developed west side of the river ran above 1.5 mg/L, up to 5.84 mg/L, with septic-indicating bromide in most, while the undeveloped east side ran at or below 1.43 mg/L (MBMG, Upper Gallatin hydrogeologic investigation). The Gallatin Local Water Quality District's long record shows valley nitrate slowly rising, though still below the federal limit.

Montana also has a genuine natural nitrate source: rock weathering in southwest Montana's Kootenai Formation releases nitrogen directly to groundwater (Montross and others, 2013), which is why the Bureau reads 2 mg/L, not zero, as the local impact threshold. Lewis and Clark County's mid-band showing has no comparable published study this page can cite; the Helena valley shares the irrigation-and-growth setting, and that is as far as the evidence goes.

The supported source reading is mixed — fertilizer and manure under irrigation in the Yellowstone, septic in the growth valleys, plus a real geogenic contribution — not a certified source at any individual system (Nolan and Hitt, 2006).

The general science — how nitrate moves, why some ground is vulnerable, and why the legacy lingers — is laid out with its sources on Where nitrate comes from.

Questions this page answers

What the Montana pattern does—and does not—say

Where does nitrate concentrate in Montana community water systems?

Yellowstone leads this layer with 10 reporting systems, followed by Lewis and Clark, Park, Blaine. Higher results follow the irrigated and growing valleys.

Does Montana have a natural nitrate source?

Yes — unusually, rock itself. Weathering of the Kootenai Formation in southwest Montana releases nitrogen to groundwater, documented in the Journal of Geophysical Research. That is why Montana studies treat roughly 2 mg/L, rather than near-zero, as the line between natural background and land-use impact.

Is irrigation good or bad for Yellowstone valley groundwater?

Both. Flood-irrigation recharge keeps the alluvial aquifer full and fresher than the surrounding bedrock water — the Bureau found it maintains potable water that would not otherwise exist. But the same recharge carries fertilizer and manure nitrogen down, and as subdivisions replace fields, lost recharge means less dilution.

Does a high public-system result mean a nearby private well is high?

No. It is a local sentinel, not a well-specific result. It shows that nitrogen and a transport pathway have reached groundwater in the area; a certified-lab test is still the only way to know a specific private well.

Sources and provenance

What this page rests on

  1. NitrateSmart inventory: 766 Montana community water systems with a current nitrate result in the three years from August 9, 2023 to August 9, 2026. Figures count people served by reporting systems, not measured tap exposure.
  2. Nolan BT, Hitt KJ (2006). Vulnerability of Shallow Groundwater and Drinking-Water Wells to Nitrate in the United States. Environmental Science & Technology 40(24):7834–7840.
  3. Dubrovsky NM, and others (2010). Nutrients in the Nation's Streams and Groundwater, 1992–2004. USGS Circular 1350.
  4. Montana Bureau of Mines and Geology. Groundwater Assessment: Middle Yellowstone Area (Treasure and Yellowstone Counties) — 53% of 119 alluvial wells >2 mg/L; 14 above the MCL; maximum 209 mg/L; irrigation-dominated recharge.
  5. Montana Bureau of Mines and Geology. Hydrogeologic Investigation of the Upper Gallatin River Corridor — developed west-side wells 1.5–5.84 mg/L vs undeveloped east-side ≤1.43 mg/L; septic effluent indicated by bromide.
  6. Montross GG, McGlynn BL, Montross SN, Gardner KK (2013). Nitrogen production from geochemical weathering of rocks in southwest Montana. Journal of Geophysical Research: Biogeosciences 118:1068–1078 — a geogenic nitrate source in the Kootenai Formation.
  7. Gallatin Local Water Quality District (2015). Gallatin State of the Waters Report — valley nitrate slowly increasing, remaining below the MCL.