Water hardness in South Dakota
South Dakota has a median ambient water hardness of 403 mg/L, which is 23.5 grains per gallon and classes as very hard. That is the middle of 54,835 samples across 66 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 South Dakota
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 |
|---|---|---|---|---|---|
| Brule County | 1,300 | 75.9 | Very hard | 800 to 1,400 | 65 |
| Lake County | 920 | 53.7 | Very hard | 570 to 1,300 | 546 |
| Meade County | 830 | 48.5 | Very hard | 434 to 1,110 | 1,514 |
| Clay County | 820 | 47.9 | Very hard | 650 to 1,100 | 1,306 |
| Fall River County | 780 | 45.6 | Very hard | 438 to 1,150 | 862 |
| Turner County | 774 | 45.2 | Very hard | 490 to 1,071 | 1,055 |
| Ziebach County | 749 | 43.8 | Very hard | 428 to 912 | 452 |
| Butte County | 710 | 41.5 | Very hard | 536 to 930 | 1,874 |
| Hutchinson County | 708 | 41.4 | Very hard | 450 to 1,180 | 1,161 |
| Clark County | 700 | 40.9 | Very hard | 440 to 1,100 | 941 |
| McCook County | 700 | 40.9 | Very hard | 630 to 848 | 113 |
| Haakon County | 640 | 37.4 | Very hard | 310 to 850 | 429 |
| Charles Mix County | 638 | 37.3 | Very hard | 259 to 962 | 1,465 |
| Miner County | 620 | 36.2 | Very hard | 360 to 800 | 786 |
| Buffalo County | 604 | 35.3 | Very hard | 370 to 870 | 182 |
| Bon Homme County | 600 | 35.1 | Very hard | 246 to 950 | 340 |
| Hanson County | 600 | 35.1 | Very hard | 380 to 1,200 | 425 |
| Day County | 590 | 34.5 | Very hard | 360 to 891 | 401 |
| Roberts County | 582 | 34 | Very hard | 380 to 806 | 1,282 |
| Jerauld County | 580 | 33.9 | Very hard | 340 to 940 | 310 |
| Kingsbury County | 531 | 31 | Very hard | 68 to 990 | 558 |
| Lincoln County | 520 | 30.4 | Very hard | 300 to 1,100 | 388 |
| Moody County | 520 | 30.4 | Very hard | 410 to 840 | 1,026 |
| Stanley County | 517 | 30.2 | Very hard | 260 to 980 | 171 |
| Marshall County | 513 | 30 | Very hard | 210 to 790 | 518 |
| Grant County | 510 | 29.8 | Very hard | 381 to 720 | 788 |
| Union County | 490 | 28.6 | Very hard | 380 to 610 | 894 |
| Campbell County | 480 | 28 | Very hard | 330 to 720 | 717 |
| Brookings County | 460 | 26.9 | Very hard | 380 to 600 | 1,421 |
| Deuel County | 460 | 26.9 | Very hard | 383 to 730 | 275 |
| Hamlin County | 460 | 26.9 | Very hard | 360 to 620 | 476 |
| Minnehaha County | 433 | 25.3 | Very hard | 350 to 540 | 2,533 |
| Hand County | 430 | 25.1 | Very hard | 290 to 720 | 277 |
| Walworth County | 430 | 25.1 | Very hard | 290 to 680 | 321 |
| Codington County | 425 | 24.8 | Very hard | 340 to 750 | 1,155 |
| Spink County | 417 | 24.4 | Very hard | 160 to 700 | 1,799 |
| Davison County | 416 | 24.3 | Very hard | 210 to 820 | 488 |
| Potter County | 380 | 22.2 | Very hard | 70 to 510 | 71 |
| Hyde County | 360 | 21 | Very hard | 190 to 1,200 | 103 |
| Sanborn County | 360 | 21 | Very hard | 120 to 860 | 570 |
| Brown County | 350 | 20.4 | Very hard | 257 to 501 | 1,875 |
| McPherson County | 340 | 19.9 | Very hard | 140 to 1,000 | 93 |
| Sully County | 340 | 19.9 | Very hard | 170 to 630 | 143 |
| Beadle County | 320 | 18.7 | Very hard | 161 to 580 | 4,297 |
| Edmunds County | 310 | 18.1 | Very hard | 130 to 750 | 126 |
| Dewey County | 283 | 16.5 | Very hard | 170 to 480 | 382 |
| Lawrence County | 280 | 16.4 | Very hard | 201 to 436 | 2,091 |
| Gregory County | 260 | 15.2 | Very hard | 190 to 392 | 190 |
| Hughes County | 260 | 15.2 | Very hard | 230 to 580 | 841 |
| Pennington County | 250 | 14.6 | Very hard | 180 to 406 | 2,951 |
| Douglas County | 245 | 14.3 | Very hard | 100 to 460 | 190 |
| Yankton County | 240 | 14 | Very hard | 232 to 252 | 4,417 |
| Custer County | 230 | 13.4 | Very hard | 160 to 440 | 1,238 |
| Lyman County | 228 | 13.3 | Very hard | 115 to 586 | 710 |
| Corson County | 220 | 12.9 | Very hard | 129 to 290 | 564 |
| Aurora County | 210 | 12.3 | Very hard | 86 to 750 | 480 |
| Jones County | 210 | 12.3 | Very hard | 48 to 430 | 119 |
| Oglala Lakota County | 200 | 11.7 | Very hard | 140 to 287 | 484 |
| Tripp County | 174 | 10.2 | Hard | 156 to 210 | 259 |
| Faulk County | 155 | 9.1 | Hard | 100 to 340 | 112 |
| Mellette County | 140 | 8.2 | Hard | 120 to 190 | 500 |
| Perkins County | 140 | 8.2 | Hard | 58 to 240 | 955 |
| Todd County | 140 | 8.2 | Hard | 109 to 172 | 381 |
| Bennett County | 137 | 8 | Hard | 105 to 167 | 204 |
| Harding County | 120 | 7 | Moderately hard | 17 to 410 | 810 |
| Jackson County | 120 | 7 | Moderately hard | 40 to 588 | 365 |
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 South Dakota
At 23.5 grains per gallon, a family of four would need a softener of about 64,000 grains to regenerate roughly weekly, using around 960 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.