Water hardness in Oklahoma
Oklahoma has a median ambient water hardness of 270 mg/L, which is 15.8 grains per gallon and classes as very hard. That is the middle of 97,888 samples across 77 counties.
This is ambient water, not tap water. These figures come from samples taken from wells, streams and springs by USGS, EPA and state agencies. Municipal utilities treat, blend and sometimes soften water before it reaches a tap, so a city supply can be considerably softer than the ground beneath it. Treat this as a good guide for a private well and an approximate one for city water. Your utility's annual water quality report gives the real number for a municipal tap, and a test strip gives it for yours.
Every monitored county in Oklahoma
Ranked hardest first. The middle 50% column shows how much the samples within a county vary, which matters more than the median where a county spans two geologies.
| County | mg/L | gpg | Class | Middle 50% | Samples |
|---|---|---|---|---|---|
| Harmon County | 2,200 | 128.5 | Very hard | 1,800 to 2,700 | 778 |
| Jackson County | 1,960 | 114.5 | Very hard | 1,410 to 2,990 | 425 |
| Greer County | 1,925 | 112.5 | Very hard | 1,100 to 2,600 | 866 |
| Dewey County | 1,902 | 111.1 | Very hard | 1,500 to 2,175 | 227 |
| Washita County | 1,190 | 69.5 | Very hard | 710 to 1,650 | 322 |
| Tillman County | 1,020 | 59.6 | Very hard | 700 to 1,300 | 1,241 |
| Woods County | 1,000 | 58.4 | Very hard | 770 to 1,400 | 1,060 |
| Custer County | 940 | 54.9 | Very hard | 580 to 1,300 | 1,639 |
| Beckham County | 910 | 53.2 | Very hard | 660 to 1,200 | 638 |
| Kingfisher County | 710 | 41.5 | Very hard | 409 to 1,070 | 1,241 |
| Major County | 680 | 39.7 | Very hard | 410 to 1,810 | 752 |
| Woodward County | 680 | 39.7 | Very hard | 408 to 1,439 | 1,058 |
| Alfalfa County | 660 | 38.6 | Very hard | 500 to 910 | 1,364 |
| Kiowa County | 580 | 33.9 | Very hard | 310 to 820 | 1,470 |
| Harper County | 570 | 33.3 | Very hard | 373 to 1,367 | 1,239 |
| Stephens County | 550 | 32.1 | Very hard | 410 to 650 | 306 |
| Love County | 540 | 31.5 | Very hard | 290 to 830 | 773 |
| Caddo County | 520 | 30.4 | Very hard | 340 to 840 | 4,434 |
| Jefferson County | 490 | 28.6 | Very hard | 228 to 900 | 654 |
| Payne County | 460 | 26.9 | Very hard | 273 to 680 | 3,033 |
| Roger Mills County | 460 | 26.9 | Very hard | 266 to 915 | 395 |
| Cimarron County | 448 | 26.2 | Very hard | 210 to 615 | 204 |
| Beaver County | 420 | 24.5 | Very hard | 320 to 660 | 1,126 |
| Canadian County | 412 | 24.1 | Very hard | 270 to 490 | 719 |
| Blaine County | 400 | 23.4 | Very hard | 324 to 452 | 748 |
| Grady County | 400 | 23.4 | Very hard | 260 to 700 | 2,873 |
| Garvin County | 390 | 22.8 | Very hard | 240 to 520 | 1,023 |
| Seminole County | 380 | 22.2 | Very hard | 220 to 590 | 1,913 |
| Grant County | 376 | 22 | Very hard | 280 to 540 | 401 |
| McClain County | 370 | 21.6 | Very hard | 260 to 462 | 551 |
| Carter County | 360 | 21 | Very hard | 250 to 500 | 2,075 |
| Kay County | 340 | 19.9 | Very hard | 198 to 490 | 2,782 |
| Logan County | 330 | 19.3 | Very hard | 230 to 439 | 1,652 |
| Garfield County | 320 | 18.7 | Very hard | 200 to 460 | 313 |
| Noble County | 310 | 18.1 | Very hard | 175 to 458 | 595 |
| Murray County | 304 | 17.8 | Very hard | 263 to 330 | 1,784 |
| Hughes County | 300 | 17.5 | Very hard | 197 to 410 | 2,888 |
| Marshall County | 297 | 17.4 | Very hard | 227 to 355 | 145 |
| Ellis County | 288 | 16.8 | Very hard | 248 to 520 | 252 |
| Lincoln County | 280 | 16.4 | Very hard | 188 to 335 | 1,094 |
| Pawnee County | 280 | 16.4 | Very hard | 200 to 360 | 2,143 |
| Creek County | 270 | 15.8 | Very hard | 180 to 540 | 1,084 |
| Oklahoma County | 270 | 15.8 | Very hard | 197 to 353 | 3,146 |
| Pontotoc County | 261 | 15.2 | Very hard | 194 to 315 | 294 |
| Tulsa County | 260 | 15.2 | Very hard | 180 to 370 | 3,881 |
| Johnston County | 250 | 14.6 | Very hard | 186 to 305 | 962 |
| Haskell County | 240 | 14 | Very hard | 130 to 500 | 3,027 |
| Texas County | 240 | 14 | Very hard | 220 to 320 | 427 |
| Pottawatomie County | 235 | 13.7 | Very hard | 140 to 308 | 478 |
| Okmulgee County | 220 | 12.9 | Very hard | 140 to 310 | 2,235 |
| Bryan County | 219 | 12.8 | Very hard | 152 to 275 | 945 |
| Cleveland County | 210 | 12.3 | Very hard | 150 to 307 | 2,451 |
| Nowata County | 202 | 11.8 | Very hard | 160 to 250 | 1,039 |
| Cotton County | 200 | 11.7 | Very hard | 165 to 311 | 864 |
| Ottawa County | 200 | 11.7 | Very hard | 144 to 365 | 2,183 |
| Craig County | 192 | 11.2 | Very hard | 134 to 318 | 686 |
| Osage County | 184 | 10.7 | Very hard | 139 to 245 | 1,910 |
| Muskogee County | 180 | 10.5 | Hard | 124 to 250 | 1,467 |
| Rogers County | 180 | 10.5 | Hard | 140 to 240 | 2,613 |
| Washington County | 180 | 10.5 | Hard | 131 to 240 | 1,149 |
| McIntosh County | 167 | 9.8 | Hard | 118 to 239 | 400 |
| Okfuskee County | 163 | 9.5 | Hard | 109 to 207 | 292 |
| Choctaw County | 161 | 9.4 | Hard | 102 to 236 | 356 |
| Wagoner County | 130 | 7.6 | Hard | 104 to 190 | 338 |
| Delaware County | 120 | 7 | Moderately hard | 103 to 139 | 2,425 |
| Atoka County | 119 | 7 | Moderately hard | 48 to 220 | 1,036 |
| Adair County | 110 | 6.4 | Moderately hard | 92 to 128 | 1,001 |
| Coal County | 108 | 6.3 | Moderately hard | 63 to 168 | 476 |
| Mayes County | 105 | 6.1 | Moderately hard | 87 to 130 | 1,500 |
| Cherokee County | 100 | 5.8 | Moderately hard | 84 to 122 | 1,771 |
| Sequoyah County | 82 | 4.8 | Moderately hard | 66 to 96 | 1,303 |
| Comanche County | 78 | 4.6 | Moderately hard | 48 to 202 | 393 |
| Pittsburg County | 66 | 3.9 | Moderately hard | 41 to 114 | 841 |
| Le Flore County | 36 | 2.1 | Soft | 16 to 120 | 2,555 |
| Latimer County | 33 | 1.9 | Soft | 22 to 60 | 436 |
| Pushmataha County | 20 | 1.2 | Soft | 15 to 29 | 960 |
| McCurtain County | 19 | 1.1 | Soft | 12 to 49 | 1,768 |
Source: Water Quality Portal (USGS, EPA and state agencies), waterqualitydata.us, retrieved 2026-09-19. 2,904,346 samples across 3,110 counties.
What this means for a household in Oklahoma
At 15.8 grains per gallon, a family of four would need a softener of about 40,000 grains to regenerate roughly weekly, using around 648 lb of salt a year. Size it for your own household.
66 of these counties include well samples, so the figures are a reasonable guide for private well water there. Municipal supplies in the same counties may be softer, because utilities often blend or treat.
Hardness follows geology rather than borders. Where a county sits on limestone or dolomite the water is hard; on granite, basalt or sandstone it is soft. That is why neighbouring counties in this table can differ by a factor of several.