Measured, not modelled
Measured well-water hardness for Idaho, county by county: the median of laboratory hardness samples taken at real water wells, in grains per gallon and mg/L as CaCO3, with the number of wells behind every figure.
Most published hardness-by-county tables are estimates from municipal tap water. The figures below are different: they are medians of laboratory samples taken at water wells, from the public record, and every row says how many wells stand behind it. The same table qualifies every lead Hard Water Feed sells, so this page is also how you check our arithmetic — the full method is on the methodology page.
Ratings below use the Water Quality Association scale, in grains per gallon (gpg); 1 gpg is 17.118 mg/L as CaCO3.
| Rating | Range |
|---|---|
| soft | 0 – 1 gpg |
| slightly hard | 1 – 3.5 gpg |
| moderately hard | 3.5 – 7 gpg |
| hard | 7 – 10.5 gpg |
| very hard | over 10.5 gpg |
Source: Water Quality Portal (USGS & US EPA). Water Quality Portal (USGS NWIS + EPA STORET), siteType Well, 13 analytes. 4979 wells filed a hardness value; 440 had it computed from calcium + magnesium. 522 local cells, 18 counties. 26 counties dropped for straddling the softener threshold. A county appears only when at least 3 distinct wells carry a laboratory hardness result; the 26 of Idaho’s 44 counties not listed fall short of that bar or fall under the note above, and they are left out rather than guessed at.
| County | Median (gpg) | Middle half (gpg) | mg/L CaCO3 | Rating | Wells | Samples |
|---|---|---|---|---|---|---|
| Adams | 3.3 | 2.6–4.5 | 56 | slightly hard | 31 | 31 |
| Bannock | 17 | 12.2–19.8 | 291 | very hard | 117 | 117 |
| Bear Lake | 17.1 | 14.5–19.8 | 293 | very hard | 45 | 45 |
| Bingham | 12.8 | 9.3–14.4 | 219 | very hard | 206 | 206 |
| Blaine | 10.3 | 8.5–11.8 | 176 | hard | 115 | 115 |
| Boise | 2.1 | 1.3–3.4 | 36 | slightly hard | 28 | 28 |
| Bonneville | 13.4 | 9.5–15.2 | 229 | very hard | 117 | 117 |
| Butte | 10.5 | 9.2–12.9 | 180 | very hard | 343 | 343 |
| Camas | 2.9 | 2.1–3.5 | 50 | slightly hard | 43 | 43 |
| Caribou | 32.4 | 22.8–49.2 | 555 | very hard | 160 | 160 |
| Franklin | 17.8 | 13.2–21.5 | 305 | very hard | 30 | 30 |
| Gooding | 9.7 | 8.3–13 | 166 | hard | 94 | 94 |
| Jerome | 13.4 | 10.2–15.1 | 229 | very hard | 129 | 129 |
| Minidoka | 15 | 12–18.6 | 257 | very hard | 143 | 143 |
| Oneida | 18.7 | 14.6–26.9 | 320 | very hard | 118 | 118 |
| Power | 13.1 | 11.1–18.1 | 224 | very hard | 115 | 115 |
| Teton | 10.9 | 8.6–12.9 | 187 | very hard | 42 | 42 |
| Valley | 1.6 | 0.9–2.3 | 27 | slightly hard | 61 | 61 |
Yes — the median across 343 measured wells, one reading each in Butte County is 10.5 grains per gallon (about 180 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 9.2 and 12.9 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 206 measured wells, one reading each in Bingham County is 12.8 grains per gallon (about 219 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 9.3 and 14.4 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 160 measured wells, one reading each in Caribou County is 32.4 grains per gallon (about 555 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 22.8 and 49.2 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 143 measured wells, one reading each in Minidoka County is 15 grains per gallon (about 257 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 12 and 18.6 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 129 measured wells, one reading each in Jerome County is 13.4 grains per gallon (about 229 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 10.2 and 15.1 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 118 measured wells, one reading each in Oneida County is 18.7 grains per gallon (about 320 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 14.6 and 26.9 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 117 measured wells, one reading each in Bannock County is 17 grains per gallon (about 291 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 12.2 and 19.8 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 117 measured wells, one reading each in Bonneville County is 13.4 grains per gallon (about 229 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 9.5 and 15.2 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 115 measured wells, one reading each in Blaine County is 10.3 grains per gallon (about 176 mg/L as CaCO3), which is “hard” on the Water Quality Association scale. The middle half of those wells falls between 8.5 and 11.8 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median across 115 measured wells, one reading each in Power County is 13.1 grains per gallon (about 224 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. The middle half of those wells falls between 11.1 and 18.1 gpg, so individual wells vary widely around the median. This is groundwater measured at other wells in the county, not a reading from any one property.
The answers above cover the 10 counties with the most measured wells; the table covers every county that clears the minimum. If your county isn’t listed, the honest answer is that the public record doesn’t hold enough well samples there for us to say — not that its water is soft.
Hard Water Feed publishes a weekly feed of newly filed domestic wells in these counties, qualified against this same hardness table and sold to one water-treatment business per territory. The territory grid shows what’s open; the category guide explains the mechanism.
Selling water treatment in Idaho? The new wells behind these figures are sold by territory — well water leads in Idaho.
Built from the same data that builds the feed, and regenerated with it — figures on this page change only when the underlying public record does.