Hard Water Map

Montana Water Hardness by County

Water in Montana has a median hardness of 183 mg/L as CaCO₃ — "very hard" on the USGS scale — based on 84,286 measurements at 14,986 monitoring stations. Rosebud County has the state's hardest measured water (820 mg/L); Ravalli County the softest (30.5). Rank: #16 of the 50 states and D.C.

Montana water hardness map — what the numbers mean. Data verified 2026-07-22.

Of Montana's 56 measured counties, 33 very hard, 11 hard, 10 moderately hard, and 2 soft. The hardest are Rosebud County (820 mg/L), Petroleum County (691.5), and Powder River County (579). Ravalli County is the softest at 30.5 mg/L (soft).

About 64% of Montana's roughly 1.1 million residents in counties with gate-passing hardness data live where tap water is hard or worse.

Statewide, Montana's median works out to 10.7 grains per gallon and ranks #16 of the 50 states and D.C. Across 84,286 measurements at 14,986 stations — 38,413 of them since 2000 — the middle 80% of readings fall between 38.5 and 809 mg/L. The public record runs from 1908 to 2026.

See where Montana sits nationally on the national map, or what its number means on the hardness scale.

Download the Montana water hardness map (PNG) — Water hardness by county in Montana: 56 counties mapped from USGS/EPA data, statewide median 183 mg/L (very hard); darker counties have harder water.

By county

Water hardness by county

The table lists all 56 measured Montana counties, hardest first. Their medians span 820 mg/L in Rosebud County to 30.5 in Ravalli County — a 26.9× range.

County water hardness, hardest first — median mg/L as CaCO₃.
CountyMedianBandResultsSitesNewest
Rosebud County820Very hard15,6831,6802025
Petroleum County691.5Very hard6211062016
Powder River County579Very hard1,5664812026
Wibaux County570Very hard169662013
Musselshell County540Very hard6732212026
Toole County434Very hard107742026
Golden Valley County424Very hard361852016
Sheridan County420Very hard3892332026
Teton County378Very hard4801442026
Dawson County359Very hard3571822018
Carter County351Very hard1971052017
Custer County340Very hard2,3352072026
Wheatland County338Very hard300612026
Phillips County324Very hard2,5963232026
Big Horn County320Very hard3,0407192026
Treasure County320Very hard723742018
Fallon County294Very hard3531412026
Cascade County290Very hard2,4862292026
Daniels County290Very hard588802026
Fergus County280Very hard6573482026
Blaine County278Very hard1,7042422026
Prairie County270Very hard296862018
McCone County260Very hard8062182019
Roosevelt County244Very hard8952882023
Liberty County240Very hard316732013
Richland County240Very hard1,4661932026
Valley County240Very hard1,0902342026
Pondera County238Very hard251912012
Meagher County195Very hard8291652026
Powell County191Very hard2,2272722026
Chouteau County190Very hard5601192026
Garfield County185.5Very hard169932026
Judith Basin County184Very hard3141722026
Yellowstone County178Hard1,7293172026
Carbon County170Hard1,6252822026
Silver Bow County166Hard2,4461712025
Deer Lodge County154Hard3,9521592026
Madison County153Hard1,6604402026
Broadwater County150Hard6051482026
Gallatin County140Hard1,7345772026
Hill County140Hard5491212016
Beaverhead County134Hard1,6916532026
Granite County130Hard1,0052032026
Lewis and Clark County122Hard4,5237482026
Missoula County112Moderately hard3,4263052026
Sweet Grass County106Moderately hard2991312026
Lake County105Moderately hard4581502026
Glacier County100Moderately hard1,4343262026
Lincoln County99Moderately hard3,0254082026
Mineral County93.2Moderately hard358522026
Flathead County87.8Moderately hard1,8844032026
Sanders County86.7Moderately hard1,9022242026
Stillwater County78Moderately hard8471632026
Park County72Moderately hard1,2573042026
Jefferson County46Soft2,7386402026
Ravalli County30.5Soft5352562026

ZIP codes

ZIP codes in Montana

The ZIP codes below are grouped by the Montana county they fall in. Each ZIP takes its county's measured median — shown in the group header — so this is a ZIP-to-county guide, not a separate reading for every ZIP. To check the water system serving a specific address, use the lookup.

Rosebud County · 820 mg/L · Very hard

59012†59039†59043†59054†59083†59323†59327†59333†59347†

Petroleum County · 691.5 mg/L · Very hard

59087†

Powder River County · 579 mg/L · Very hard

59003†59062†59314†59316†59317†59343†59351†

Wibaux County · 570 mg/L · Very hard

59353†

Musselshell County · 540 mg/L · Very hard

59059†59072†

Toole County · 434 mg/L · Very hard

59435†59444†59454†59466†59474†59482†59484†

Golden Valley County · 424 mg/L · Very hard

59046†59074†

Sheridan County · 420 mg/L · Very hard

59211†59219†59242†59247†59252†59254†59256†59257†59258†59275†

Teton County · 378 mg/L · Very hard

59419†59422†59433†59436†59467†59468†

Dawson County · 359 mg/L · Very hard

59259†59315†59330†59339†

Carter County · 351 mg/L · Very hard

59311†59319†59324†59332†

Custer County · 340 mg/L · Very hard

59301†59336†59338†59345†

Wheatland County · 338 mg/L · Very hard

59036†59078†59085†59453†

Phillips County · 324 mg/L · Very hard

59261†59524†59537†59538†59544†59546†

Big Horn County · 320 mg/L · Very hard

59016†59022†59025†59031†59034†59035†59050†59064†59066†59075†59089†

Treasure County · 320 mg/L · Very hard

59010†59038†59076†

Fallon County · 294 mg/L · Very hard

59313†59344†59354†

Cascade County · 290 mg/L · Very hard

5940159404†59405†59412†59414†59421†59443†59463†59465†59472†59477†59480†59483†59485†59487†

Daniels County · 290 mg/L · Very hard

59222†59253†59263†59276†

Fergus County · 280 mg/L · Very hard

59032†59424†59430†59441†59451†59457†59464†59471†59489†

Blaine County · 278 mg/L · Very hard

59523†59526†59527†59529†59535†59542†59547†

Prairie County · 270 mg/L · Very hard

59326†59349†

McCone County · 260 mg/L · Very hard

59214†59215†59223†59274†

Roosevelt County · 244 mg/L · Very hard

59201†59212†59213†59218†59226†59255†

Liberty County · 240 mg/L · Very hard

59456†5946159522†59531†59545†

Richland County · 240 mg/L · Very hard

59217†59221†59243†59262†59270†

Valley County · 240 mg/L · Very hard

59225†59230†5923159240†59241†59244†59248†59250†59260†59273†

Pondera County · 238 mg/L · Very hard

594165942559432†59448†59486†

Meagher County · 195 mg/L · Very hard

59053†59642†59645†

Powell County · 191 mg/L · Very hard

59713†59722†59728†59731†59733†59843†59854†

Chouteau County · 190 mg/L · Very hard

59420†59440†59442†59446†59450†59460†59520†

Garfield County · 185.5 mg/L · Very hard

59058†59077†59312†59318†59322†59337†

Judith Basin County · 184 mg/L · Very hard

59418†59447†59452†59462†59469†59479†

Yellowstone County · 178 mg/L · Hard

59002†59006†59015†59024†59037†59044†59079†59088†59101†5910259105†59106†

Carbon County · 170 mg/L · Hard

59007†59008†59013†59014†59026†59029†59041†59068†59070†59071†

Silver Bow County · 166 mg/L · Hard

59701†59727†59748†59750†

Deer Lodge County · 154 mg/L · Hard

59711†59756†59762†

Madison County · 153 mg/L · Hard

59710†5971659720†59729†59735†59740†59745†59747†59749†59751†59754†59755†

Broadwater County · 150 mg/L · Hard

59643†59644†59647†

Gallatin County · 140 mg/L · Hard

59714†59715†59718†59730†59741†59752†59758†59760†

Hill County · 140 mg/L · Hard

59501†59521†59525†59528†59530†59532†59540†

Beaverhead County · 134 mg/L · Hard

59724†59725†59732†59736†59739†59743†59746†59761†

Granite County · 130 mg/L · Hard

59825†59832†59837†59858†

Lewis and Clark County · 122 mg/L · Hard

59410†59601†59602†596235962559633†59635†59636†59639†59640†59648†

Missoula County · 112 mg/L · Moderately hard

5980159802†59803†59804†59808†5981259821†59823†59826†59834†59846†59847†5985159868†

Sweet Grass County · 106 mg/L · Moderately hard

59011†59033†59052†59055†

Lake County · 105 mg/L · Moderately hard

59824†5985559860†59863†59864†59865†59910†59911†59914†59915†59929†59931†

Glacier County · 100 mg/L · Moderately hard

59411†59417†59427†59434†

Lincoln County · 99 mg/L · Moderately hard

59917†59918†59923†59930†59933†59934†59935†

Mineral County · 93.2 mg/L · Moderately hard

59820†59830†59842†59866†59867†59872†

Flathead County · 87.8 mg/L · Moderately hard

59901†59912†59913†59916†5991959920†5992259925†59926†59927†59928†59932†59936†59937†

Sanders County · 86.7 mg/L · Moderately hard

59831†59844†59845†59848†59853†59856†59859†59873†59874†

Stillwater County · 78 mg/L · Moderately hard

59001†5901959028†59057†59061†59063†59067†59069†

Park County · 72 mg/L · Moderately hard

59018†59020†59027†59030†59047†59065†59081†59082†59086†

Jefferson County · 46 mg/L · Soft

59631†59632†59634†59638†59721†59759†

Ravalli County · 30.5 mg/L · Soft

59827†59828†59829†59833†59840†59841†59870†59871†59875†

† 353 ZIP codes are not served by a mapped community water system — most are private-well areas. See well water hardness.

Check any ZIP's utility and hardness →

Source

Groundwater vs surface water

Montana's groundwater measures harder than its surface water — 318 mg/L across 22,107 samples versus 170 across 60,789, about 1.9× harder. Wells draw from groundwater, so well owners in Montana tend to see the harder number — 318 mg/L, very hard. Groundwater readings there run 33 to 1580 mg/L across the middle 80% of samples. The comparison draws on 6,950 groundwater and 7,900 surface-water monitoring sites; 9,009 readings above 2,000 mg/L were logged but held out of the medians as outliers.

Groundwater (wells)

318 mg/L as CaCO₃ · 22,107 results at 6,950 stations.

Surface water (rivers, lakes)

170 mg/L as CaCO₃ · 60,789 results at 7,900 stations.

Groundwater measures about 1.9× harder than surface water here.

Chemistry

Water chemistry in Montana

Beyond the hardness number, Montana's water carries a fuller chemical signature — here is how its measured parameters compare to national benchmarks.

TDS

2210 mg/L · n=28,989

2210 mg/L — about 9.8× the national county median of 226, consistent with hard, mineral-rich water.

pH

7.8 pH · n=45,182

pH 7.8 — within the EPA secondary range of 6.5–8.5, on the alkaline side.

Alkalinity

242 mg/L as CaCO3 · n=38,066

242 mg/L — substantial buffering capacity, which resists pH swings.

Calcium : Magnesium

63 : 23 mg/L ≈ 2.74 : 1 · n=48,774

Calcium is about 62% of Montana's hardness (63 mg/L Ca to 23 mg/L Mg), a little more magnesium-rich than the national ~68% calcium share.

Parameter medians may include a small share of quality-control samples; the hardness lane is fully QC-filtered.

Aquifers

Major aquifers under Montana

3 aquifer systems supply much of Montana's measured groundwater.

  • Alluvial aquifers — median 356 mg/L across 72 samples at 63 sites: very hard.
  • Lower Tertiary aquifers — median 242.5 mg/L across 64 samples at 43 sites: very hard.
  • Northern Rocky Mountains Intermontane Basins aquifer systems — median 105.7 mg/L across 30 samples at 26 sites: moderately hard.

Together these systems account for 166 measured samples at 132 sites. Aquifer medians pool samples across a whole system and can mask local variation — see the national aquifer map for how these compare across states.

Trend

Hardness over time

1910s2020s390

Montana's decade median moved from 280 mg/L in the 1910s to 177 in the 2020s. Over the series, the decade median peaked at 390 mg/L in the 1950s and bottomed at 132 in the 2000s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.

Scale

Where Montana sits on the scale

On the USGS scale, Montana's 183 mg/L is very hard — 10.7 grains per gallon, well above the 180 mg/L very-hard cutoff — among the hardest water measured in the US.

SoftModerately hardHardVery hard60 · 3.5 gpg120 · 7.0 gpg180 · 10.5 gpg183 mg/L — Very hard
Harder than 59% of the 2,977 measured county medians.

At 183 mg/L (10.7 gpg), water-softener owners in Montana typically set their unit to this hardness — settings calculator.

Questions

Frequently asked questions

Is Montana's water hard?
Montana's median hardness is 183 mg/L as CaCO₃, "very hard" on the USGS scale and 1.31× the national county median of 140 mg/L. About 64% of residents in measured counties have hard-or-worse water.
Which county in Montana has the hardest water?
Rosebud County, with a median of 820 mg/L as CaCO₃ across 15,683 measurements.
Is well water harder than city water in Montana?
Groundwater measures harder here — about 1.9× the surface water — so wells tend to run harder (groundwater 318 vs surface water 170 mg/L).
How do I find my exact hardness in Montana?
Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
Is Montana's water harder than the national average?
Yes. Montana's median of 183 mg/L is 1.31× the national county median of 140 mg/L, and Montana ranks #16 of the 50 states and D.C.

Compare

States with similar hardness

Two states measure closest to Montana's 183 mg/L: Missouri at 196 mg/L and Michigan at 168 mg/L. Montana measures harder than 70% of states. Browse the full ranking on the statistics page.

More: hardness scale · check your address · national statistics · the national map.

By . Source: USGS/EPA Water Quality Portal — 84,286 Montana measurements. Data last verified . Methodology.

Cite this page: “Montana Water Hardness by County.” Hard Water Map. Retrieved 2026-07-22, https://hardwatermap.com/water-hardness/montana/