Why does water hardness vary across Idaho?

Water hardness varies across Idaho because utilities can use different groundwater wells, reservoirs, treatment plants, blends, and distribution zones. Private wells can also differ from nearby municipal water.

What city in Idaho has the hardest water?

Preston has the hardest water among higher-confidence Idaho city pages at 327 PPM. Check the city page for local systems and ZIP codes before making treatment decisions.

Does this include municipal water, well water, or both?

The state report combines public water system records, utility reports, and USGS monitoring where available. Municipal treated-water records are preferred when present. Private well hardness can vary at the address level and should be confirmed with a local test.

How many water systems are in Idaho?

Idaho has 764 active community water systems serving 252 cities.

Water Hardness in Idaho

Average: 157 PPMModerately Hard252 cities764 water systems

State report

Is Idaho Water Hard or Soft?

Idaho water is moderately hard on average at 157 PPM (9.2 GPG). Local readings can vary by utility, aquifer, treatment plant, and private well use.

State average

157 PPM

Moderately Hard

Local coverage

252 cities

764 water systems

Source profile

247 ZIPs

direct or USGS-backed

93% of covered ZIPs use treated-water records or USGS monitoring, so the state report has relatively strong source support.

Methodology Data sources Search by ZIP code

State data profile

How to read the Idaho results

State pages are screening and comparison hubs. They summarize ZIP, city, and water-system patterns so you can find the local page that best matches your home or utility.

Direct or USGS-backed ZIPs

247 of 267

93% use treated-water records or USGS monitoring.

Estimated ZIP values

20 ZIPs

7% use nearby, county, or state-level fallback values.

Dataset update

March 9, 2026

Source coverage and rollups are rebuilt from the public dataset.

Use the source coverage below to judge how much local confirmation a specific city or ZIP needs. The methodology page explains the source hierarchy, weighting, and limitations.

State Average

157 PPM

Moderately Hard

Coverage

252 cities

764 water systems in the state rollup.

Data Source Coverage

ZIP-level source mix for Idaho; higher direct and USGS coverage means less reliance on regional estimates.

267 ZIPs covered

Verified treated water

Utility, CCR, or state treated-water records

24%

64 ZIPs

High-confidence USGS

Environmental monitoring matched to local systems

69%

183 ZIPs

Estimated

Nearby, county, or state-level fallback values

20 ZIPs

In Idaho, 24% of ZIPs use verified treated-water records, 69% use high-confidence USGS monitoring, and 7% use estimates that should be confirmed locally for treatment decisions.

What the Data Shows in Idaho

Hard water is common but not universal in Idaho: 42% of classified ZIPs are hard or very hard.

Idaho is mostly supported by high-confidence USGS monitoring, which is useful for regional hardness patterns and should be interpreted as environmental monitoring rather than a direct treated tap-water report for every home.

Use the city table below to compare local results. For estimated locations or unusually high readings, confirm with your utility or a home hardness test before sizing treatment equipment.

ZIP Hardness Distribution

Soft10% (27)

Slightly Hard32% (85)

Moderately Hard16% (43)

Hard32% (85)

Very Hard10% (27)

Treatment Takeaway

Idaho has a mixed hardness profile. Some areas may benefit from softening, while others may only need point-of-use filtration or no hardness treatment at all.

How to Use This Data

The source coverage is relatively strong in Idaho, so these pages are useful for comparing local patterns before confirming your home's exact hardness.

Source-Backed Water Systems in Idaho

Large systems with treated-water reports or USGS monitoring behind the state rollup.

Review source labels

Water system	Hardness	Source label	Population
Capitol Water Corp ID4010022 - Ada County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	9,000
Idoc Sbx Complex ID4010141 - Ada County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	3,309
Idoc Idaho State Correctional Center ID4010240 - Ada County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	2,204
Hillsdale Estates Homeowners Assn ID4010218 - Ada County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	800
Rustic Acres Mobile Home Park ID4010126 - Ada County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	540
Wilderness Ranch Owners Association Inc ID4080055 - Boise County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	525
Idoc Mountain View Transformation Center ID4010255 - Ada County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	456
Flying H Trailer Ranch ID4010062 - Ada County	115 PPM Slightly Hard	Annual Water Quality Report Verified - Annual Water Quality Report	430

Useful Idaho City Pages

Shortcuts to city pages backed by more ZIP-code or water-system data.

Cities With More Local Data

Boise

9 ZIPs · 38 systems

Slightly Hard (108 PPM)

Nampa

3 ZIPs · 37 systems

Moderately Hard (150 PPM)

Moderately Hard (150 PPM)

Coeur D Alene

2 ZIPs · 22 systems

Moderately Hard (122 PPM)

Pocatello

2 ZIPs · 9 systems

Hard (200 PPM)

Prioritize cities with multiple ZIPs and systems, then use the local source badges to compare high-confidence USGS readings against estimated areas.

Top 10 Hardest Water Cities

#	City	Hardness
1	Preston	Very Hard (327 PPM)
2	Burley	Very Hard (294 PPM)
3	Shelley	Very Hard (252 PPM)
4	Blackfoot	Hard (236 PPM)
5	Jerome	Hard (220 PPM)
6	Salmon	Hard (217 PPM)
7	Rexburg	Hard (204 PPM)
8	Rigby	Hard (204 PPM)
9	Ammon	Hard (201 PPM)
10	Chubbuck	Hard (201 PPM)

Top 10 Softest Water Cities

#	City	Hardness
1	Garden Valley	Soft (31 PPM)
2	Saint Maries	Slightly Hard (69 PPM)
3	Bonners Ferry	Slightly Hard (70 PPM)
4	Kamiah	Slightly Hard (84 PPM)
5	Potlatch	Slightly Hard (94 PPM)
6	Priest River	Slightly Hard (94 PPM)
7	South Gate Plaza	Slightly Hard (101 PPM)
8	Sagle	Slightly Hard (101 PPM)
9	Hope	Slightly Hard (102 PPM)
10	Coolin	Slightly Hard (103 PPM)

All Cities in Idaho

City pages marked Estimated use fallback values and should be confirmed with local testing or utility data.

AcequiaHard AhsahkaModerately Hard AlbionVery Hard AlmoVery Hard American FallsHard AmmonHard ArbonHard ArcoModerately Hard ArimoHard AshtonHard AtholModerately Hard Atomic CityHard AverySoft BancroftVery Hard BanksSlightly Hard BasaltHard BayviewModerately Hard BellevueModerately Hard BernHard BlackfootHard BlanchardSlightly Hard BlissVery Hard BloomingtonHard BoiseSlightly Hard Bonners FerrySlightly Hard BovillSlightly Hard BuhlHard BurleyVery Hard CalderSoft CaldwellModerately Hard CambridgeSlightly Hard CareyHard CareywoodSlightly Hard CarmenHard CastlefordHard CataldoModerately Hard ChallisVery Hard ChesterHard ChubbuckHard Clark ForkSlightly Hard ClarkiaSlightly Hard ClaytonSoft ClearwaterSoft CliftonHard CocolallaSlightly Hard Coeur D AleneModerately Hard CoolinSlightly Hard CorralSlightly Hard CottonwoodSoft CouncilSlightly Hard CraigmontModerately Hard CuldesacSlightly Hard DaytonHard DearySlightly Hard DecloVery Hard DesmetSlightly Hard DietrichHard DixieSoft DonnellySoft DowneyHard DriggsHard DuboisModerately Hard EagleSlightly Hard EastportSlightly Hard EdenHard Elk HornHard Elk RiverSoft EllisHard FairfieldSoft FeltHard FerdinandModerately Hard FernwoodSlightly Hard FilerHard FirthHard Fish HavenHard Fort HallHard FranklinHard FruitlandSlightly Hard Garden CitySlightly Hard Garden ValleySoft GeneseeSlightly Hard GenevaHard GeorgetownVery Hard GibbonsvilleHard Glenns FerrySoft GoodingVery Hard GraceVery Hard Grand ViewVery Hard GrangevilleSlightly Hard GrasmereModerately Hard GreencreekSlightly Hard GreenleafModerately Hard HagermanModerately Hard HaileyHard HamerHard HammettSoft HansenHard HarrisonModerately Hard HarvardSlightly Hard Hayden LakeSlightly Hard HazeltonHard HeyburnVery Hard Hill CitySlightly Hard HolbrookHard HomedaleVery Hard HopeSlightly Hard Horseshoe BendSoft HoweHard Idaho CitySoft Idaho FallsHard Indian ValleySlightly Hard InkomHard IonaHard IrwinHard Island ParkHard JeromeHard JuliaettaSlightly Hard KamiahSlightly Hard KelloggSoft KendrickSlightly Hard KimberlyHard King HillSoft KingstonSlightly Hard KunaSlightly Hard LacledeSlightly Hard LapwaiSlightly Hard Lava Hot SpringsHard LeadoreHard LemhiHard LenoreSlightly Hard LewisvilleHard LowmanSlightly Hard LucileSlightly Hard MackayModerately Hard Macks InnHard Malad CityVery Hard MarsingVery Hard Mc CallSoft Mc CammonHard MedimontModerately Hard MelbaModerately Hard MenanHard MeridianSlightly Hard MesaSlightly Hard MiddletonModerately Hard MidvaleSlightly Hard MonteviewVery Hard MontourModerately Hard MontpelierVery Hard MooreHard MoscowSlightly Hard Mountain HomeSoft Mountain Home ASlightly Hard Moyie SpringsVery Hard MullanSlightly Hard MurraySoft MurtaughHard NafVery Hard NampaModerately Hard NaplesSlightly Hard New MeadowsSoft New PlymouthModerately Hard NewdaleModerately Hard NezperceModerately Hard NordmanSlightly Hard North ForkHard NotusModerately Hard OakleyVery Hard ObsidianModerately Hard OlaSlightly Hard Old TownSlightly Hard OreanaSlightly Hard OrofinoModerately Hard OsburnSlightly Hard ParisHard ParmaModerately Hard PattersonHard PaulVery Hard PayetteModerately Hard PeckSlightly Hard PicaboModerately Hard PierceSoft PinehurstSlightly Hard PingreeHard PlacervilleSlightly Hard PlummerSlightly Hard PocatelloHard PollockSlightly Hard PonderaySlightly Hard Post FallsModerately Hard PotlatchSlightly Hard PrestonVery Hard Priest RiverSlightly Hard PrincetonSlightly Hard RathdrumModerately Hard ReubensModerately Hard RexburgHard RichfieldModerately Hard RigbyHard RigginsVery Hard RirieHard RobertsHard RocklandVery Hard RogersonHard SagleSlightly Hard Saint AnthonySlightly Hard Saint CharlesHard Saint MariesSlightly Hard SalmonHard SandpointSlightly Hard SantaSlightly Hard ShelleyVery Hard ShoshoneHard ShoupSoft SilvertonSlightly Hard SmeltervilleSlightly Hard Soda SpringsVery Hard South Gate PlazaSlightly Hard SpencerHard Spirit LakeModerately Hard SpringfieldHard StanleySoft StarSlightly Hard SterlingHard StitesSlightly Hard Sugar CityHard Sun ValleyModerately Hard Swan ValleyHard SwanlakeHard SweetSlightly Hard TendoyHard TensedSlightly Hard TerretonHard TetonHard TetoniaHard ThatcherHard TroySlightly Hard Twin FallsHard VictorHard ViolaSlightly Hard WallaceSoft WayanHard WeippeSlightly Hard WeiserSlightly Hard WendellModerately Hard West MountainSoft WestonVery Hard White BirdSoft WilderModerately Hard WinchesterSlightly Hard WorleyModerately Hard Yellow PineSoft