Hard Water Map

South Dakota Water Hardness by County

Water in South Dakota has a median hardness of 391.4 mg/L as CaCO₃ — "very hard" on the USGS scale — based on 54,706 measurements at 23,553 monitoring stations. Brule County has the state's hardest measured water (1300 mg/L); Harding County the softest (94.4). Rank: #1 of the 50 states and D.C.

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

Of South Dakota's 56 measured counties, 48 very hard, 6 hard, and 2 moderately hard. The hardest are Brule County (1300 mg/L), Meade County (820), and Clay County (808.5). Harding County is the softest at 94.4 mg/L (moderately hard).

About 100% of South Dakota's roughly 0.9 million residents in counties with gate-passing hardness data live where tap water is hard or worse.

Statewide, South Dakota's median works out to 22.9 grains per gallon and ranks #1 of the 50 states and D.C. Across 54,706 measurements at 23,553 stations — 6,397 of them since 2000 — the middle 80% of readings fall between 116 and 1100 mg/L. The public record runs from 1900 to 2023.

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

Download the South Dakota water hardness map (PNG) — Water hardness by county in South Dakota: 56 counties mapped from USGS/EPA data, statewide median 391.4 mg/L (very hard); darker counties have harder water.

By county

Water hardness by county

The table lists all 56 measured South Dakota counties, hardest first. Their medians span 1300 mg/L in Brule County to 94.4 in Harding County — a 13.8× range. 10 more South Dakota counties lack gate-passing data.

County water hardness, hardest first — median mg/L as CaCO₃.
CountyMedianBandResultsSitesNewest
Brule County1300Very hard65422007
Meade County820Very hard1,5073702021
Clay County808.5Very hard1,3038162014
Fall River County770Very hard8553012018
Turner County753Very hard1,0457102014
Ziebach County745Very hard449732014
McCook County700Very hard106222014
Butte County697Very hard1,8711832023
Hutchinson County690Very hard1,1525622014
Haakon County640Very hard427482020
Charles Mix County617Very hard1,4593182022
Buffalo County612Very hard177852014
Bon Homme County590Very hard3381942005
Roberts County580Very hard1,2699592022
Hanson County560Very hard4232232014
Grant County510Very hard7825402014
Moody County510Very hard1,0774622021
Lincoln County500Very hard3882642004
Marshall County500Very hard5183872014
Union County490Very hard8935692014
Stanley County482Very hard170562014
Campbell County480Very hard7114932019
Brookings County460Very hard1,4128432014
Deuel County460Very hard2741832013
Hamlin County460Very hard4742872014
Minnehaha County432Very hard2,4875972014
Hand County430Very hard2772112001
Walworth County430Very hard3212642016
Codington County423.2Very hard1,1506562014
Davison County410Very hard4852992014
Spink County390Very hard1,7881,1822014
Sanborn County360Very hard5705142004
Brown County343.5Very hard1,8664922014
Beadle County320Very hard4,2752,2212014
Edmunds County310Very hard126812001
Dewey County281Very hard379882014
Lawrence County273Very hard2,1892762023
Gregory County260Very hard190772014
Hughes County260Very hard8223902020
Pennington County250Very hard2,9395162023
Douglas County245Very hard1901422002
Yankton County240Very hard4,4034692019
Custer County230Very hard1,2343522021
Lyman County226.5Very hard7041562020
Corson County218.2Very hard5601072018
Jones County206Very hard119312014
Aurora County200Very hard4804302004
Oglala Lakota County200Very hard4831092010
Tripp County173Hard2571072014
Faulk County150Hard112622001
Todd County140.5Hard3792782016
Mellette County140Hard4941062014
Perkins County140Hard9533212010
Bennett County137Hard2041371995
Jackson County97Moderately hard364752010
Harding County94.4Moderately hard8085712012

ZIP codes

ZIP codes in South Dakota

The ZIP codes below are grouped by the South Dakota 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.

Brule County · 1300 mg/L · Very hard

57325†5735557370

Meade County · 820 mg/L · Very hard

57706†57718†57719†57737†57741†57748†57758†57761†57767†57769†5778557787†57791†57792†

Clay County · 808.5 mg/L · Very hard

570105706957073

Fall River County · 770 mg/L · Very hard

5773557747577635776657782

Turner County · 753 mg/L · Very hard

57014570155702157036570435705357070

Ziebach County · 745 mg/L · Very hard

5762257623

McCook County · 700 mg/L · Very hard

570125704757048570585731957374†

Butte County · 697 mg/L · Very hard

57717†57760†5776257788†

Hutchinson County · 690 mg/L · Very hard

57029570455705257331573545736657376

Haakon County · 640 mg/L · Very hard

575525755357567

Charles Mix County · 617 mg/L · Very hard

57329573425735657361573675736957380

Buffalo County · 612 mg/L · Very hard

5733957341

Bon Homme County · 590 mg/L · Very hard

5705957062570635706657315

Roberts County · 580 mg/L · Very hard

56219†57224572275725557257572605726257279

Hanson County · 560 mg/L · Very hard

573115733257340

Grant County · 510 mg/L · Very hard

572165724657251†5725257256†57259572645726557266†57269

Moody County · 510 mg/L · Very hard

57017570245702857065

Lincoln County · 500 mg/L · Very hard

570045701357027570325703457039570645707757108

Marshall County · 500 mg/L · Very hard

572325724757270574215743057454

Union County · 490 mg/L · Very hard

57001570255703857049

Stanley County · 482 mg/L · Very hard

5753257537

Campbell County · 480 mg/L · Very hard

5763257646

Brookings County · 460 mg/L · Very hard

57002570065700757026570615707157220†57276

Deuel County · 460 mg/L · Very hard

57213572185722657234†572375723857268

Hamlin County · 460 mg/L · Very hard

5722157223572415724257248

Minnehaha County · 432 mg/L · Very hard

57003570055701857020570225703057033570355704157055570685710357104571055710657107571105711757197

Hand County · 430 mg/L · Very hard

573625737157373573815746757470

Walworth County · 430 mg/L · Very hard

57420574525747257631

Codington County · 423.2 mg/L · Very hard

572015723557243572455726357272

Davison County · 410 mg/L · Very hard

573015733457363

Spink County · 390 mg/L · Very hard

57424574295743457436574405746157465574695747657477

Sanborn County · 360 mg/L · Very hard

573145735957385

Brown County · 343.5 mg/L · Very hard

5740157426574275743257433574395744157445†574465744957460574745747957481

Beadle County · 320 mg/L · Very hard

5731257322†573245734857350573795738457386

Edmunds County · 310 mg/L · Very hard

574285745157471

Dewey County · 281 mg/L · Very hard

57601576255763057636576525765657661

Lawrence County · 273 mg/L · Very hard

57732†57754†57759†57779†57783†57793†57799†

Gregory County · 260 mg/L · Very hard

573175733557523575335753857571

Hughes County · 260 mg/L · Very hard

575015752257536

Pennington County · 250 mg/L · Very hard

57701†57702†57703†5772557745†577515777557780†57790

Douglas County · 245 mg/L · Very hard

5731357328573305734457364

Yankton County · 240 mg/L · Very hard

57031570375704057046570675707257078

Custer County · 230 mg/L · Very hard

57730577385774457773

Lyman County · 226.5 mg/L · Very hard

573655754457548575685756957576

Corson County · 218.2 mg/L · Very hard

57621†5763357634†57639†57641†57642†57645†57657†57658†57659†57660†

Jones County · 206 mg/L · Very hard

575315755957562

Aurora County · 200 mg/L · Very hard

573685737557383

Oglala Lakota County · 200 mg/L · Very hard

57716†57722†57752†57756†57764†57770†57772†57794†

Tripp County · 173 mg/L · Hard

575285752957534575415758057584

Faulk County · 150 mg/L · Hard

57435574385746657473

Todd County · 140.5 mg/L · Hard

5755557563575665757057572

Mellette County · 140 mg/L · Hard

57521575605757957585

Perkins County · 140 mg/L · Hard

5762057626†57638576405764457649

Bennett County · 137 mg/L · Hard

57551†57574†57714†

Jackson County · 97 mg/L · Moderately hard

57543†57547†57577†57750†

Harding County · 94.4 mg/L · Moderately hard

57650†57651†57720†57724†57755†57776†

† 70 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

South Dakota's groundwater measures harder than its surface water — 460 mg/L across 28,533 samples versus 339.8 across 25,949, about 1.4× harder. Wells draw from groundwater, so well owners in South Dakota tend to see the harder number — 460 mg/L, very hard. Groundwater readings there run 69 to 1200 mg/L across the middle 80% of samples. The comparison draws on 22,413 groundwater and 1,089 surface-water monitoring sites; 1,070 readings above 2,000 mg/L were logged but held out of the medians as outliers.

Groundwater (wells)

460 mg/L as CaCO₃ · 28,533 results at 22,413 stations.

Surface water (rivers, lakes)

339.8 mg/L as CaCO₃ · 25,949 results at 1,089 stations.

Groundwater measures about 1.4× harder than surface water here.

Chemistry

Water chemistry in South Dakota

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

TDS

764 mg/L · n=14,597

764 mg/L — about 3.4× the national county median of 226, consistent with hard, mineral-rich water.

pH

8.3 pH · n=10,495

pH 8.3 — within the EPA secondary range of 6.5–8.5, on the alkaline side.

Alkalinity

200 mg/L as CaCO3 · n=14,926

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

Calcium : Magnesium

82 : 38.7 mg/L ≈ 2.12 : 1 · n=14,541

Calcium is about 56% of South Dakota's hardness (82 mg/L Ca to 38.7 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 South Dakota

3 aquifer systems supply much of South Dakota's measured groundwater.

  • Alluvial aquifers — median 555 mg/L across 29 samples at 18 sites: very hard.
  • Sand and gravel aquifers (glaciated regions) — median 500 mg/L across 9,254 samples at 6,479 sites: very hard.
  • Paleozoic aquifers — median 290 mg/L across 1,008 samples at 568 sites: very hard.

Together these systems account for 10,291 measured samples at 7,065 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

1930s2020s610

South Dakota's decade median moved from 346.5 mg/L in the 1930s to 565 in the 2020s. Over the series, the decade median peaked at 610 mg/L in the 1940s and bottomed at 244 in the 1990s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.

Scale

Where South Dakota sits on the scale

On the USGS scale, South Dakota's 391.4 mg/L is very hard — 22.9 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 gpg391.4 mg/L — Very hard
Harder than 92% of the 2,977 measured county medians.

At 391.4 mg/L (22.9 gpg), water-softener owners in South Dakota typically set their unit to this hardness — settings calculator.

Questions

Frequently asked questions

Is South Dakota's water hard?
South Dakota's median hardness is 391.4 mg/L as CaCO₃, "very hard" on the USGS scale and 2.8× the national county median of 140 mg/L. About 100% of residents in measured counties have hard-or-worse water.
Which county in South Dakota has the hardest water?
Brule County, with a median of 1300 mg/L as CaCO₃ across 65 measurements. Even the softest, Harding County at 94.4 mg/L, is still "moderately hard" on the USGS scale.
Is well water harder than city water in South Dakota?
Groundwater measures harder here — about 1.4× the surface water — so wells tend to run harder (groundwater 460 vs surface water 339.8 mg/L).
How do I find my exact hardness in South Dakota?
Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
Is South Dakota's water harder than the national average?
Yes. South Dakota's median of 391.4 mg/L is 2.8× the national county median of 140 mg/L, and South Dakota ranks #1 of the 50 states and D.C.

Compare

States with similar hardness

Two states measure closest to South Dakota's 391.4 mg/L: Iowa at 310 mg/L and North Dakota at 310 mg/L. South Dakota measures harder than 100% 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 — 54,706 South Dakota measurements. Data last verified . Methodology.

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