Hard Water Map

Oklahoma Water Hardness by County

Water in Oklahoma has a median hardness of 260 mg/L as CaCO₃ — "very hard" on the USGS scale — based on 97,469 measurements at 6,695 monitoring stations. Harmon County has the state's hardest measured water (1780 mg/L); McCurtain County the softest (19.4). Rank: #10 of the 50 states and D.C.

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

Of Oklahoma's 77 measured counties, 60 very hard, 5 hard, 8 moderately hard, and 4 soft. The hardest are Harmon County (1780 mg/L), Dewey County (1700), and Jackson County (1470). McCurtain County is the softest at 19.4 mg/L (soft).

About 89% of Oklahoma's roughly 4 million residents in counties with gate-passing hardness data live where tap water is hard or worse.

Statewide, Oklahoma's median works out to 15.2 grains per gallon and ranks #10 of the 50 states and D.C. Across 97,469 measurements at 6,695 stations — 32,316 of them since 2000 — the middle 80% of readings fall between 79 and 850 mg/L. The public record runs from 1907 to 2026.

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

Download the Oklahoma water hardness map (PNG) — Water hardness by county in Oklahoma: 77 counties mapped from USGS/EPA data, statewide median 260 mg/L (very hard); darker counties have harder water.

By county

Water hardness by county

The table lists all 77 measured Oklahoma counties, hardest first. Their medians span 1780 mg/L in Harmon County to 19.4 in McCurtain County — a 91.8× range.

County water hardness, hardest first — median mg/L as CaCO₃.
CountyMedianBandResultsSitesNewest
Harmon County1780Very hard778432011
Dewey County1700Very hard227352023
Jackson County1470Very hard4221152025
Greer County1200Very hard866582025
Washita County1090Very hard322512025
Tillman County1009Very hard1,237242025
Woods County950Very hard1,060782024
Custer County870Very hard1,631802025
Beckham County860Very hard638692025
Alfalfa County650Very hard1,364572024
Kingfisher County650Very hard1,2411262024
Woodward County590Very hard1,0581312024
Kiowa County571Very hard1,471902025
Stephens County545Very hard306292021
Harper County540Very hard1,239622024
Love County530Very hard758162025
Caddo County510Very hard4,4312462025
Major County510Very hard7521212024
Jefferson County480Very hard650222025
Payne County460Very hard3,031922024
Roger Mills County450Very hard394532025
Cimarron County448Very hard204712021
Beaver County419.3Very hard1,124602024
Canadian County410.5Very hard7171682023
Grady County400Very hard2,8701812025
Blaine County390Very hard744692018
Garvin County390Very hard1,022562025
Grant County370Very hard401572024
McClain County370Very hard550872025
Seminole County362Very hard1,9171612025
Carter County360Very hard2,030192025
Kay County340Very hard2,779592024
Logan County330Very hard1,6501892024
Garfield County320Very hard313502024
Noble County308Very hard595462024
Murray County304Very hard1,7821282025
Marshall County297Very hard14582025
Hughes County290Very hard2,888212025
Ellis County285.4Very hard252572024
Lincoln County280Very hard1,0862652025
Pawnee County280Very hard2,141302024
Oklahoma County270Very hard3,1204962025
Creek County266Very hard1,0851532025
Pontotoc County260Very hard294632025
Tulsa County260Very hard3,881222025
Johnston County250Very hard9621032025
Haskell County240Very hard3,024922025
Texas County240Very hard4261052021
Pottawatomie County233Very hard4782362025
Okmulgee County220Very hard2,234132025
Bryan County216.7Very hard926342025
Cleveland County210.5Very hard2,4463692025
Cotton County200Very hard815232025
Nowata County200Very hard1,039242023
Craig County190.9Very hard686782023
Ottawa County190Very hard2,1821952023
Osage County184Very hard1,9092672024
Muskogee County180Very hard1,460562025
Rogers County180Very hard2,611542013
Washington County180Very hard1,149152018
McIntosh County166Hard400182025
Okfuskee County162.5Hard292392025
Choctaw County160.5Hard356202025
Wagoner County130Hard338152023
Delaware County120Hard2,3941092026
Atoka County118.5Moderately hard1,036682025
Adair County110Moderately hard992332025
Coal County107Moderately hard475442025
Mayes County104.5Moderately hard1,494372025
Cherokee County100Moderately hard1,749532025
Sequoyah County81.5Moderately hard1,302312025
Comanche County78Moderately hard3921042025
Pittsburg County66Moderately hard841572025
Le Flore County36Soft2,5311172026
Latimer County33Soft436372025
Pushmataha County20Soft944472025
McCurtain County19.4Soft1,684882025

ZIP codes

ZIP codes in Oklahoma

The ZIP codes below are grouped by the Oklahoma county each mostly falls within (by land area). Each ZIP takes that 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.

Key: a † after a ZIP means it has no mapped community water system — usually a private-well area. Plain ZIPs are served by a mapped community water system.

Harmon County · 1780 mg/L · Very hard

735447355073571

Dewey County · 1700 mg/L · Very hard

73658†7365973663†7366773724†7383573859†

Jackson County · 1470 mg/L · Very hard

73521735237352673532†7353773539735497355673560†

Greer County · 1200 mg/L · Very hard

73547†73554†73673

Washita County · 1090 mg/L · Very hard

730217302473622†73624†73626736327364173647†7366173664

Tillman County · 1009 mg/L · Very hard

73530†7354273546735517355373555†73570†

Woods County · 950 mg/L · Very hard

73716†7371773731†7374673842†73860†

Custer County · 870 mg/L · Very hard

730967360173620736257363973669

Beckham County · 860 mg/L · Very hard

73627736447364573662†73668

Alfalfa County · 650 mg/L · Very hard

73719†7372273726†7372873739†73741†73749†

Kingfisher County · 650 mg/L · Very hard

7301673734†73742†737507375673764

Woodward County · 590 mg/L · Very hard

73801†73852†7385373857†

Kiowa County · 571 mg/L · Very hard

730417306273559†73564735667365173655

Stephens County · 545 mg/L · Very hard

7305573425†73434†7344273491†7352973533

Harper County · 540 mg/L · Very hard

7383473855†

Love County · 530 mg/L · Very hard

73430†73441†734487345373459

Caddo County · 510 mg/L · Very hard

73001†730057300673009†73015730177302973033†730387304273047†73048†73053†

Major County · 510 mg/L · Very hard

73718737297373773747†737607376873838†

Jefferson County · 480 mg/L · Very hard

73456735207356573569†73573

Payne County · 460 mg/L · Very hard

740237403274059†74062†74074†74075740777407874085

Roger Mills County · 450 mg/L · Very hard

73628†7363873642†736507365473660†73666

Cimarron County · 448 mg/L · Very hard

73933†73937†73946†73947†

Beaver County · 419.3 mg/L · Very hard

73844†73848†73931†73932†73938†73950†

Canadian County · 410.5 mg/L · Very hard

730147302273036†73064†730787309073099†73762

Grady County · 400 mg/L · Very hard

73002†73004†73010†73011†7301873059†730677307973082†7308973092

Blaine County · 390 mg/L · Very hard

73040†73043†73646†7374473755†7376373770†73772†

Garvin County · 390 mg/L · Very hard

73052730577307473075730987343374872†

Grant County · 370 mg/L · Very hard

73758†737597376173766737717463674643

McClain County · 370 mg/L · Very hard

730317306573080730937309574831†

Seminole County · 362 mg/L · Very hard

74830748377484074849†74867†7486874884

Carter County · 360 mg/L · Very hard

73401734357343673437†734387344373444†73458†734637348173487†73488

Kay County · 340 mg/L · Very hard

74601†746317463274641746467464774653

Logan County · 330 mg/L · Very hard

7302573027†730287304473050†73058†73063

Garfield County · 320 mg/L · Very hard

7305673701†73703737057372073727†73730†73733†73735†73736737387374373753737547377374640

Noble County · 308 mg/L · Very hard

73061730737307773757746307464474651†

Murray County · 304 mg/L · Very hard

73030†73032†73086

Marshall County · 297 mg/L · Very hard

7343973440†73446

Hughes County · 290 mg/L · Very hard

745317457074827748397484874850†74883

Ellis County · 285.4 mg/L · Very hard

73832†73840†73841†73843†73851†73858†

Lincoln County · 280 mg/L · Very hard

74026†740797482474832†7483474855†7486474869†7487574881†

Pawnee County · 280 mg/L · Very hard

7402074034740457405874081†

Oklahoma County · 270 mg/L · Very hard

7300373007†7300873012730137302073034†73045†730497305473066†73084†73097†73102731037310473105731067310773108731097311073111731127311473115731167311773118731197312073121†731227312773128†731297313073131†731327313473135†7313973141†73142731457314973150†73151731597316273169†73179

Creek County · 266 mg/L · Very hard

74010†74028†7403074038†74039740417404474046†74050†740527406674068†7407174131

Pontotoc County · 260 mg/L · Very hard

74820748257484274843†7484474865†74871

Tulsa County · 260 mg/L · Very hard

74008740117401274021740337403774055740637410374104741057410674107†74108741107411274114741157411674117†7411974120741287412974130†741327413374134741357413674137741457414674171

Johnston County · 250 mg/L · Very hard

7343273447†73450734557346073461†74530†74748†74836†74856

Haskell County · 240 mg/L · Very hard

744627447274552749417494374944†

Texas County · 240 mg/L · Very hard

7390173939†73942†73944†73945†73949†73951†

Pottawatomie County · 233 mg/L · Very hard

748017480474826†748517485274854†7486674873†74878†

Okmulgee County · 220 mg/L · Very hard

740477442174431744377444574447†7445674460

Bryan County · 216.7 mg/L · Very hard

734497470174720†7472174723†74726†74729†74730747317473374741†74747†74753

Cleveland County · 210.5 mg/L · Very hard

73019†73026†73051†73068†73069†73070†7307173072†7316073165†7317073173†74857†

Cotton County · 200 mg/L · Very hard

735287353173548735627356873572

Nowata County · 200 mg/L · Very hard

7402774042740487407274083

Craig County · 190.9 mg/L · Very hard

743017433274333†7434974369†

Ottawa County · 190 mg/L · Very hard

74339†74343†7435474358743607436374370†

Osage County · 184 mg/L · Very hard

740017400274003†74035†74054†74056†74060†74070†74073†74084†74126†741277460474633†74637†74650†74652

Muskogee County · 180 mg/L · Very hard

744017440374422†744237443474436744507445574463†744687446974470†

Rogers County · 180 mg/L · Very hard

74015740167401774019740367405374080

Washington County · 180 mg/L · Very hard

7400674022†7402974051†74061†74082

McIntosh County · 166 mg/L · Hard

744267442874432744387445974845†

Okfuskee County · 162.5 mg/L · Hard

74829748337485974860†74880

Choctaw County · 160.5 mg/L · Hard

7472774735†74738†7474374756†74759†74761

Wagoner County · 130 mg/L · Hard

7401474429†7444674454744587446774477

Delaware County · 120 mg/L · Hard

7433174338†743427434474346†743477435974364†74368†

Atoka County · 118.5 mg/L · Moderately hard

74525†7453374540†745557456974576†

Adair County · 110 mg/L · Moderately hard

749317496074964†74965†

Coal County · 107 mg/L · Moderately hard

74534†745357453874556†74572†

Mayes County · 104.5 mg/L · Moderately hard

743307433774340743507435274361†7436574366†74367

Cherokee County · 100 mg/L · Moderately hard

74427†7444174451†74452†74457†7446474471

Sequoyah County · 81.5 mg/L · Moderately hard

7443574936749457494674948749547495574962

Comanche County · 78 mg/L · Moderately hard

7350173503†7350573507†735277353873540†73541†73543735527355773567

Pittsburg County · 66 mg/L · Moderately hard

744257443074442745017452274528†7454674547†745537455474560†7456174565

Le Flore County · 36 mg/L · Soft

74549†74577†74901†74902749307493274935749377493974940749427494774949749517495374956†74957†74959†74966

Latimer County · 33 mg/L · Soft

745637457174578

Pushmataha County · 20 mg/L · Soft

7452174523745367454374557†7455874562†74567†74574†74760

McCurtain County · 19.4 mg/L · Soft

74722†74724†74728†74734†74736747377474074745747507475474755†74764†74766†74963†

† 241 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

Oklahoma's surface water measures harder than its groundwater — 265 mg/L across 92,013 samples versus 230 across 5,415, about 1.2× harder. For well owners that is the better side of a hard bargain: at 230 mg/L, Oklahoma groundwater is still very hard, and most of the state's drinking water is pumped from it. Groundwater readings there run 40.3 to 700 mg/L across the middle 80% of samples. The comparison draws on 3,977 groundwater and 2,709 surface-water monitoring sites; 2,700 readings above 2,000 mg/L were logged but held out of the medians as outliers.

Groundwater (wells)

230 mg/L as CaCO₃ · 5,415 results at 3,977 stations.

Surface water (rivers, lakes)

265 mg/L as CaCO₃ · 92,013 results at 2,709 stations.

Surface water measures about 1.2× harder than groundwater here.

Chemistry

Water chemistry in Oklahoma

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

TDS

140.1 mg/L · n=18,213

140.1 mg/L — below the national county median of 226.

pH

8 pH · n=23,144

pH 8 — within the EPA secondary range of 6.5–8.5, on the alkaline side.

Alkalinity

134 mg/L as CaCO3 · n=57,663

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

Calcium : Magnesium

48 : 9.9 mg/L ≈ 4.85 : 1 · n=4,374

Calcium is about 75% of Oklahoma's hardness (48 mg/L Ca to 9.9 mg/L Mg), a little more calcium-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 Oklahoma

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

  • Blaine aquifer — median 1650 mg/L across 67 samples at 64 sites: very hard.
  • Alluvial aquifers — median 320 mg/L across 980 samples at 924 sites: very hard.
  • Arbuckle-Simpson aquifer — median 320 mg/L across 160 samples at 126 sites: very hard.

Together these systems account for 1,207 measured samples at 1,114 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

1940s2020s310

Oklahoma's decade median moved from 280 mg/L in the 1940s to 193 in the 2020s. Over the series, the decade median peaked at 310 mg/L in the 1970s and bottomed at 193 in the 2020s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.

Scale

Where Oklahoma sits on the scale

On the USGS scale, Oklahoma's 260 mg/L is very hard — 15.2 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 gpg260 mg/L — Very hard
Harder than 76% of the 2,977 measured county medians.

At 260 mg/L (15.2 gpg), water-softener owners in Oklahoma typically set their unit to this hardness — settings calculator.

Questions

Frequently asked questions

Is Oklahoma's water hard?
Oklahoma's median hardness is 260 mg/L as CaCO₃, "very hard" on the USGS scale and 1.86× the national county median of 140 mg/L. About 89% of residents in measured counties have hard-or-worse water.
Which county in Oklahoma has the hardest water?
Harmon County, with a median of 1780 mg/L as CaCO₃ across 778 measurements.
Is well water harder than city water in Oklahoma?
Surface water measures harder here — about 1.2× the groundwater — so wells tend to run softer (groundwater 230 vs surface water 265 mg/L).
How do I find my exact hardness in Oklahoma?
Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
Is Oklahoma's water harder than the national average?
Yes. Oklahoma's median of 260 mg/L is 1.86× the national county median of 140 mg/L, and Oklahoma ranks #10 of the 50 states and D.C.

Compare

States with similar hardness

Two states measure closest to Oklahoma's 260 mg/L: Kansas at 260 mg/L and Ohio at 270 mg/L. Oklahoma measures harder than 82% 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 — 97,469 Oklahoma measurements. Data last verified . Methodology.

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