Water Hardness in South Dakota
Across 2 measured cities — with 95 more covered by labeled county-level estimates — South Dakota's median tap water hardness is 121.5 mg/L (7.1 gpg): hard on the USGS scale. Below: every covered city, the state's hardest and softest water, and the geology that explains it.
Data updated September 13, 2026. Sources: utility-reported water quality data and USGS/EPA Water Quality Portal samples.
What it costs to soften South Dakota water
Water softener cost in South Dakota at 7.1 gpg prices the equipment and the installation labour against the plumber wages published for South Dakota, and labels every range as modelled or measured rather than leaving you to guess which it is.
South Dakota · 7.11 grains per gallon
$923–$1,146
installed, midpoint $1,022 — a 24,000-grain unit, the size 4 people at this hardness need.
Salt and drain water over 10 years: $733–$1,377 — the 7,785,450 grains of hardness this household removes, at the national salt price and water rate whose sources are named below. Filter changes and Service contract are omitted rather than assumed.
Sized for 4 people regenerating every 7 days: 14,931 grains of capacity needed, rounded up to the next common residential size. The median of 2 measured South Dakota cities in our hardness dataset. Modelled: the standard build band published for that state at the size this hardness calls for, equipment priced 2026-10-04 against the May 2025 reference period (OEWS M2025). Salt: the median retailer price of 3 retailers, read 2026-10-04, at a declared salt dose per regeneration. Drain water: about 50 gallons per regeneration from a government extension estimate read 2026-10-04, at the 2024 national average water and sewer rate from a government source read 2026-10-04.
Deciding whether it is worth it at all? Start from how much a water softener costs nationally — the same equipment, installation and ten-year ownership breakdown before any state wage adjustment is applied.
South Dakota Cities by Hardness Category
Measured cities only — labeled county estimates never enter the category counts or the median.
| Category | Range | Measured cities | Share |
|---|---|---|---|
| Soft | 0-60 mg/L | 0 | 0.0% |
| Moderately hard | 60-120 mg/L | 1 | 50.0% |
| Hard | 120-180 mg/L | 1 | 50.0% |
| Very hard | >180 mg/L | 0 | 0.0% |
Hardest and Softest Water in South Dakota
Measured values only; labeled county estimates and values under active dispute never rank.
Hardest water in South Dakota
- Rapid City — 124.0 mg/L (7.3 gpg), hard
- Sioux Falls — 119.0 mg/L (7.0 gpg), moderately hard
Softest water in South Dakota
- Sioux Falls — 119.0 mg/L (7.0 gpg), moderately hard
- Rapid City — 124.0 mg/L (7.3 gpg), hard
Every Covered City in South Dakota
All 97 covered South Dakota cities, sorted by population served. "County estimate" rows are labeled context values from USGS/EPA Water Quality Portal county sampling — they never enter the median above. City names link to each city's full water quality page.
| City | Hardness (mg/L) | gpg | Category | Data |
|---|---|---|---|---|
| Sioux Falls | 119.0 | 7.0 | Moderately hard | Utility-reported |
| Rapid City | 124.0 | 7.3 | Hard | Utility-reported |
| Watertown | 379.5 | 22.2 | Very hard | County estimate |
| Brookings | 500.0 | 29.2 | Very hard | County estimate |
| Dell Rapids | 477.0 | 27.9 | Very hard | County estimate |
| Yankton | 380.0 | 22.2 | Very hard | County estimate |
| Pierre | 270.0 | 15.8 | Very hard | County estimate |
| Spearfish | 320.0 | 18.7 | Very hard | County estimate |
| Vermillion | 831.0 | 48.6 | Very hard | County estimate |
| Box Elder | 830.0 | 48.5 | Very hard | County estimate |
| Brandon | 477.0 | 27.9 | Very hard | County estimate |
| Harrisburg | 980.0 | 57.3 | Very hard | County estimate |
| Murdo | 228.0 | 13.3 | Very hard | County estimate |
| Tea | 980.0 | 57.3 | Very hard | County estimate |
| Egan | 460.0 | 26.9 | Very hard | County estimate |
| Wakonda | 831.0 | 48.6 | Very hard | County estimate |
| Beresford | 980.0 | 57.3 | Very hard | County estimate |
| North Sioux City | 506.0 | 29.6 | Very hard | County estimate |
| Canton | 980.0 | 57.3 | Very hard | County estimate |
| Mobridge | 405.0 | 23.7 | Very hard | County estimate |
| Hartford | 477.0 | 27.9 | Very hard | County estimate |
| Eagle Butte | 405.0 | 23.7 | Very hard | County estimate |
| Mitchell | 529.0 | 30.9 | Very hard | County estimate |
| Kimball | 185.0 | 10.8 | Very hard | County estimate |
| Lennox | 980.0 | 57.3 | Very hard | County estimate |
| Sisseton | 740.0 | 43.3 | Very hard | County estimate |
| Chamberlain | 185.0 | 10.8 | Very hard | County estimate |
| Flandreau | 460.0 | 26.9 | Very hard | County estimate |
| Redfield | 568.0 | 33.2 | Very hard | County estimate |
| Clark | 782.5 | 45.8 | Very hard | County estimate |
| Fort Pierre | 752.0 | 44.0 | Very hard | County estimate |
| Springfield | 240.0 | 14.0 | Very hard | County estimate |
| Custer | 210.0 | 12.3 | Very hard | County estimate |
| Elk Point | 506.0 | 29.6 | Very hard | County estimate |
| Volga | 500.0 | 29.2 | Very hard | County estimate |
| Webster | 837.4 | 49.0 | Very hard | County estimate |
| Wagner | 740.0 | 43.3 | Very hard | County estimate |
| Mission | 148.5 | 8.7 | Hard | County estimate |
| Newell | 733.0 | 42.9 | Very hard | County estimate |
| Groton | 454.5 | 26.6 | Very hard | County estimate |
| Fort Thompson | 590.5 | 34.5 | Very hard | County estimate |
| Lower Brule | 265.7 | 15.5 | Very hard | County estimate |
| Salem | 814.5 | 47.6 | Very hard | County estimate |
| Oral | 695.0 | 40.6 | Very hard | County estimate |
| Gregory | 368.0 | 21.5 | Very hard | County estimate |
| Deadwood | 320.0 | 18.7 | Very hard | County estimate |
| Crooks | 477.0 | 27.9 | Very hard | County estimate |
| Clear Lake | 440.0 | 25.7 | Very hard | County estimate |
| Platte | 740.0 | 43.3 | Very hard | County estimate |
| Baltic | 477.0 | 27.9 | Very hard | County estimate |
| Garretson | 477.0 | 27.9 | Very hard | County estimate |
| Lemmon | 260.0 | 15.2 | Very hard | County estimate |
| Worthing | 980.0 | 57.3 | Very hard | County estimate |
| Tyndall | 240.0 | 14.0 | Very hard | County estimate |
| Alcester | 506.0 | 29.6 | Very hard | County estimate |
| Edgemont | 695.0 | 40.6 | Very hard | County estimate |
| Estelline | 440.0 | 25.7 | Very hard | County estimate |
| Highmore | 260.6 | 15.2 | Very hard | County estimate |
| Faulkton | 150.2 | 8.8 | Hard | County estimate |
| Selby | 199.0 | 11.6 | Very hard | County estimate |
| Hot Springs | 695.0 | 40.6 | Very hard | County estimate |
| Colman | 460.0 | 26.9 | Very hard | County estimate |
| Lead | 320.0 | 18.7 | Very hard | County estimate |
| Presho | 265.7 | 15.5 | Very hard | County estimate |
| Lake Norden | 445.0 | 26.0 | Very hard | County estimate |
| Wolsey | 520.0 | 30.4 | Very hard | County estimate |
| Timber Lake | 405.0 | 23.7 | Very hard | County estimate |
| Herreid | 489.0 | 28.6 | Very hard | County estimate |
| Tabor | 240.0 | 14.0 | Very hard | County estimate |
| Irene | 380.0 | 22.2 | Very hard | County estimate |
| Gayville | 380.0 | 22.2 | Very hard | County estimate |
| Hayti | 445.0 | 26.0 | Very hard | County estimate |
| Blunt | 270.0 | 15.8 | Very hard | County estimate |
| Ethan | 529.0 | 30.9 | Very hard | County estimate |
| Belle Fourche | 733.0 | 42.9 | Very hard | County estimate |
| Alpena | 520.0 | 30.4 | Very hard | County estimate |
| Black Hawk | 830.0 | 48.5 | Very hard | County estimate |
| Trent | 460.0 | 26.9 | Very hard | County estimate |
| Mission Hill | 380.0 | 22.2 | Very hard | County estimate |
| Wessington | 330.0 | 19.3 | Very hard | County estimate |
| Huron | 520.0 | 30.4 | Very hard | County estimate |
| Volin | 380.0 | 22.2 | Very hard | County estimate |
| Buffalo Gap | 180.0 | 10.5 | Hard | County estimate |
| Scotland | 240.0 | 14.0 | Very hard | County estimate |
| Lesterville | 380.0 | 22.2 | Very hard | County estimate |
| Oelrichs | 695.0 | 40.6 | Very hard | County estimate |
| Java | 199.0 | 11.6 | Very hard | County estimate |
| Elkton | 500.0 | 29.2 | Very hard | County estimate |
| Miller | 330.0 | 19.3 | Very hard | County estimate |
| Wallace | 379.5 | 22.2 | Very hard | County estimate |
| Carpenter | 520.0 | 30.4 | Very hard | County estimate |
| Fairburn | 210.0 | 12.3 | Very hard | County estimate |
| Batesland | 180.0 | 10.5 | Hard | County estimate |
| Emery | 546.0 | 31.9 | Very hard | County estimate |
| Martin | 150.0 | 8.8 | Hard | County estimate |
| Philip | 805.0 | 47.1 | Very hard | County estimate |
| Piedmont | 830.0 | 48.5 | Very hard | County estimate |
Above 120 mg/L (7 gpg), scale is usually worth treating — see our water softener guide, or size a system with the hardness calculator & converter.
The Geology Behind South Dakota's Water Hardness
South Dakota sits in the Great Plains and interior lowlands region.
The Great Plains and interior lowlands are underlain by carbonate rock, gypsum, and other evaporite deposits, and the semi-arid climate concentrates dissolved minerals rather than flushing them out. Aquifers like the High Plains (Ogallala) yield water the USGS classifies as hard to very hard across most of the region, from the Dakotas down through Texas. Surface-water systems fed by plains rivers carry much of the same mineral load.
Source: USGS - High Plains aquifer
South Dakota Water Hardness FAQ
Does South Dakota have hard water?
Yes — across South Dakota's measured cities, typical tap water is hard. The median is 121.5 mg/L (7.1 gpg) — hard on the USGS scale, where anything above 120 mg/L (7 gpg) counts as hard. 1 of South Dakota's 2 measured cities fall in the hard or very hard bands (50%), so check your own city rather than the state average.
How hard is tap water in South Dakota?
Across the 2 South Dakota cities with measured values in our index, the median hardness is 121.5 mg/L (7.1 gpg) — hard on the USGS scale. Individual cities range from 119.0 to 124.0 mg/L, so check your own city rather than assuming the state number.
Which city in South Dakota has the hardest water?
Rapid City has the hardest measured tap water in our South Dakota index at 124.0 mg/L (7.3 gpg) — hard on the USGS scale. Rankings use measured utility values only; labeled county estimates and values under active dispute are excluded.
Do I need a water softener in South Dakota?
1 of South Dakota's 2 measured cities (50%) fall in the hard or very hard bands — above 120 mg/L (7 gpg), the level where most water treatment professionals suggest considering an ion-exchange softener. Hardness varies utility to utility, so look up your own city's value before sizing equipment.
How do I find my city's exact water hardness?
Enter your ZIP code in our free lookup at tapwaterdata.com/zip to see the value we hold for your South Dakota city from utility-reported water quality data, check your water utility's annual Consumer Confidence Report (CCR), or use a home test-strip kit.
Need whole-house or professional water treatment?
For the problems a pitcher or under-sink filter cannot fix — scale, rust and black staining, sulfur smell, well contamination, or test results you cannot explain. Tell us what is happening and we will connect you with a local water-treatment professional.
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