Water Hardness in Idaho
Across 29 measured cities — with 71 more covered by labeled county-level estimates — Idaho's median tap water hardness is 118.5 mg/L (6.9 gpg): moderately hard on the USGS scale. Below: every covered city, the state's hardest and softest water, and the geology that explains it.
Data updated July 6, 2026. Sources: utility-reported water quality data and USGS/EPA Water Quality Portal samples.
Idaho 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 | 3 | 10.3% |
| Moderately hard | 60-120 mg/L | 14 | 48.3% |
| Hard | 120-180 mg/L | 6 | 20.7% |
| Very hard | >180 mg/L | 6 | 20.7% |
Hardest and Softest Water in Idaho
Measured values only; labeled county estimates and values under active dispute never rank.
Hardest water in Idaho
- Soda Springs — 556.0 mg/L (32.5 gpg), very hard
- Twin Falls — 400.0 mg/L (23.4 gpg), very hard
- Pocatello — 351.0 mg/L (20.5 gpg), very hard
- Chubbuck — 340.0 mg/L (19.9 gpg), very hard
- Filer — 336.0 mg/L (19.6 gpg), very hard
Softest water in Idaho
- Boise City — 89.5 mg/L (5.2 gpg), moderately hard
- Garden City — 89.5 mg/L (5.2 gpg), moderately hard
- Eagle — 90.0 mg/L (5.3 gpg), moderately hard
- Kuna — 90.4 mg/L (5.3 gpg), moderately hard
- Avimor — 90.8 mg/L (5.3 gpg), moderately hard
Every Covered City in Idaho
All 100 covered Idaho 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 |
|---|---|---|---|---|
| Meridian | 85.8 | 5.0 | Moderately hard | Utility-reported |
| Kuna | 90.4 | 5.3 | Moderately hard | Utility-reported |
| Garden City | 89.5 | 5.2 | Moderately hard | Utility-reported |
| Boise City | 89.5 | 5.2 | Moderately hard | Utility-reported |
| Eagle | 90.0 | 5.3 | Moderately hard | Utility-reported |
| Avimor | 90.8 | 5.3 | Moderately hard | Utility-reported |
| Hidden Springs | 90.8 | 5.3 | Moderately hard | Utility-reported |
| Nampa | 170.0 | 9.9 | Hard | County estimate |
| Post Falls | 115.5 | 6.8 | Moderately hard | Utility-reported |
| Hayden | 118.5 | 6.9 | Moderately hard | Utility-reported |
| Hayden Lake | 121.4 | 7.1 | Hard | Utility-reported |
| Coeur D Alene | 118.4 | 6.9 | Moderately hard | Utility-reported |
| Dalton Gardens | 119.9 | 7.0 | Moderately hard | Utility-reported |
| Caldwell | 170.0 | 9.9 | Hard | County estimate |
| Idaho Falls | 173.0 | 10.1 | Hard | Utility-reported |
| Lewiston | 122.0 | 7.1 | Hard | County estimate |
| Pocatello | 351.0 | 20.5 | Very hard | Utility-reported |
| Fernan Lake Village | 120.8 | 7.1 | Hard | Utility-reported |
| Huetter | 120.8 | 7.1 | Hard | Utility-reported |
| Twin Falls | 400.0 | 23.4 | Very hard | Utility-reported |
| Sugar City | 72.4 | 4.2 | Moderately hard | County estimate |
| Chubbuck | 340.0 | 19.9 | Very hard | Utility-reported |
| Mountain Home | 192.0 | 11.2 | Very hard | County estimate |
| Star | 124.0 | 7.3 | Hard | County estimate |
| Fruitland | 212.0 | 12.4 | Very hard | County estimate |
| Blackfoot | 119.0 | 7.0 | Moderately hard | Utility-reported |
| Sandpoint | 49.0 | 2.9 | Soft | Utility-reported |
| Jerome | 231.0 | 13.5 | Very hard | County estimate |
| Ponderay | 49.0 | 2.9 | Soft | Utility-reported |
| Kootenai | 49.0 | 2.9 | Soft | Utility-reported |
| Burley | 266.5 | 15.6 | Very hard | County estimate |
| Hauser | 154.0 | 9.0 | Hard | Utility-reported |
| Middleton | 170.0 | 9.9 | Hard | County estimate |
| Bonners Ferry | 111.5 | 6.5 | Moderately hard | County estimate |
| Rathdrum | 110.0 | 6.4 | Moderately hard | Utility-reported |
| Ketchum | 129.0 | 7.5 | Hard | Utility-reported |
| Pinehurst | 37.5 | 2.2 | Soft | County estimate |
| Buhl | 290.0 | 17.0 | Very hard | County estimate |
| Kimberly | 290.0 | 17.0 | Very hard | County estimate |
| Gooding | 206.0 | 12.1 | Very hard | Utility-reported |
| Sun Valley | 159.5 | 9.3 | Hard | County estimate |
| Salmon | 172.5 | 10.1 | Hard | County estimate |
| Grangeville | 73.4 | 4.3 | Moderately hard | County estimate |
| Soda Springs | 556.0 | 32.5 | Very hard | Utility-reported |
| Heyburn | 261.0 | 15.3 | Very hard | County estimate |
| Wendell | 173.0 | 10.1 | Hard | County estimate |
| Filer | 336.0 | 19.6 | Very hard | Utility-reported |
| Fort Hall | 225.0 | 13.2 | Very hard | County estimate |
| Bellevue | 159.5 | 9.3 | Hard | County estimate |
| Boise | 124.0 | 7.3 | Hard | County estimate |
| Spirit Lake | 21.1 | 1.2 | Soft | County estimate |
| Homedale | 202.5 | 11.8 | Very hard | County estimate |
| Montpelier | 284.0 | 16.6 | Very hard | County estimate |
| Orofino | 115.0 | 6.7 | Moderately hard | County estimate |
| Wallace | 37.5 | 2.2 | Soft | County estimate |
| Parma | 170.0 | 9.9 | Hard | County estimate |
| Victor | 183.5 | 10.7 | Very hard | County estimate |
| Aberdeen | 225.0 | 13.2 | Very hard | County estimate |
| New Plymouth | 212.0 | 12.4 | Very hard | County estimate |
| Wilder | 170.0 | 9.9 | Hard | County estimate |
| Shoshone | 147.0 | 8.6 | Hard | County estimate |
| Marsing | 202.5 | 11.8 | Very hard | County estimate |
| Lapwai | 122.0 | 7.1 | Hard | County estimate |
| Driggs | 183.5 | 10.7 | Very hard | County estimate |
| Hansen | 290.0 | 17.0 | Very hard | County estimate |
| Paul | 261.0 | 15.3 | Very hard | County estimate |
| Bayview | 88.3 | 5.2 | Moderately hard | County estimate |
| Ucon | 229.0 | 13.4 | Very hard | County estimate |
| Ashton | 100.0 | 5.8 | Moderately hard | County estimate |
| Arco | 240.0 | 14.0 | Very hard | County estimate |
| Hagerman | 290.0 | 17.0 | Very hard | County estimate |
| Grace | 193.0 | 11.3 | Very hard | County estimate |
| Genesee | 111.0 | 6.5 | Moderately hard | County estimate |
| Plummer | 23.4 | 1.4 | Soft | County estimate |
| Blanchard | 88.3 | 5.2 | Moderately hard | County estimate |
| Cottonwood | 73.4 | 4.3 | Moderately hard | County estimate |
| Challis | 121.0 | 7.1 | Hard | County estimate |
| Greenleaf | 91.6 | 5.4 | Moderately hard | Utility-reported |
| Moyie Springs | 111.5 | 6.5 | Moderately hard | County estimate |
| Kooskia | 73.4 | 4.3 | Moderately hard | County estimate |
| Dover | 88.3 | 5.2 | Moderately hard | County estimate |
| Mackay | 121.0 | 7.1 | Hard | County estimate |
| Kamiah | 73.4 | 4.3 | Moderately hard | County estimate |
| Sagle | 88.3 | 5.2 | Moderately hard | County estimate |
| Bliss | 173.0 | 10.1 | Hard | County estimate |
| Bancroft | 193.0 | 11.3 | Very hard | County estimate |
| Priest River | 88.3 | 5.2 | Moderately hard | County estimate |
| Stites | 73.4 | 4.3 | Moderately hard | County estimate |
| Rupert | 261.0 | 15.3 | Very hard | County estimate |
| American Falls | 225.0 | 13.2 | Very hard | County estimate |
| Hailey | 159.5 | 9.3 | Hard | County estimate |
| White Bird | 73.4 | 4.3 | Moderately hard | County estimate |
| Notus | 170.0 | 9.9 | Hard | County estimate |
| Moscow | 111.0 | 6.5 | Moderately hard | County estimate |
| Athol | 21.1 | 1.2 | Soft | County estimate |
| Rexburg | 72.4 | 4.2 | Moderately hard | County estimate |
| Preston | 310.8 | 18.2 | Very hard | County estimate |
| Moore | 240.0 | 14.0 | Very hard | County estimate |
| Carey | 159.5 | 9.3 | Hard | County estimate |
| Cascade | 35.2 | 2.1 | Soft | 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 Idaho's Water Hardness
Idaho sits in the Mountain West basins and desert Southwest region.
Mountain snowmelt starts out soft, but across the interior West it drains into closed basins floored with carbonate and evaporite sediments, and the arid climate evaporates water faster than rain can dilute it. Rivers like the Colorado accumulate dissolved calcium and magnesium along their whole length, so the USGS maps most basin-and-range and desert-Southwest supplies as hard to very hard. Towns high in the mountains that capture snowmelt directly are the region's soft-water exceptions.
Idaho Water Hardness FAQ
Does Idaho have hard water?
On the whole, no — Idaho's statewide median sits below the hard threshold, though some cities run harder. The median is 118.5 mg/L (6.9 gpg) — moderately hard on the USGS scale, where anything above 120 mg/L (7 gpg) counts as hard. 12 of Idaho's 29 measured cities fall in the hard or very hard bands (41%), so check your own city rather than the state average.
How hard is tap water in Idaho?
Across the 29 Idaho cities with measured values in our index, the median hardness is 118.5 mg/L (6.9 gpg) — moderately hard on the USGS scale. Individual cities range from 49.0 to 556.0 mg/L, so check your own city rather than assuming the state number.
Which city in Idaho has the hardest water?
Soda Springs has the hardest measured tap water in our Idaho index at 556.0 mg/L (32.5 gpg) — very 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 Idaho?
12 of Idaho's 29 measured cities (41%) 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 Idaho city from utility-reported water quality data, check your water utility's annual Consumer Confidence Report (CCR), or use a home test-strip kit.
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