How hard is the water in Washington?

The average water hardness across Washington is 90 PPM (5.3 GPG), classified as slightly hard. Hardness varies by city - the hardest higher-confidence city page is Coupeville (289 PPM) and the softest is Arlington (12 PPM).

What city in Washington has the hardest water?

Coupeville has the hardest water among higher-confidence Washington city pages at 289 PPM. A water softener is recommended for residents.

How many water systems are in Washington?

Washington has 2,311 active community water systems serving 452 cities.

Water Hardness in Washington

Average: 90 PPMSlightly Hard452 cities2,311 water systems

State data profile

How to read the Washington 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

441 of 561

79% use treated-water records or USGS monitoring.

Estimated ZIP values

120 ZIPs

21% 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

90 PPM

Slightly Hard

Coverage

452 cities

2,311 water systems in the state rollup.

Data Source Coverage

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

561 ZIPs covered

Verified treated water

Utility, CCR, or state treated-water records

52%

293 ZIPs

High-confidence USGS

Environmental monitoring matched to local systems

26%

148 ZIPs

Estimated

Nearby, county, or state-level fallback values

21%

120 ZIPs

In Washington, 52% of ZIPs use verified treated-water records, 26% use high-confidence USGS monitoring, and 21% use estimates that should be confirmed locally for treatment decisions.

What the Data Shows in Washington

Most classified ZIPs in Washington are below the hard-water threshold, though local systems can still vary.

Washington has unusually strong treated-water coverage: 52% of ZIPs use utility, CCR, or state treated-water records.

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

Soft45% (250)

Slightly Hard30% (169)

Moderately Hard9% (49)

Hard14% (78)

Very Hard3% (15)

Treatment Takeaway

Hardness treatment is less likely to be needed statewide, but local water systems can still differ from the state pattern. Test first if you see scale or spotting.

How to Use This Data

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

Useful Washington City Pages

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

Cities With More Local Data

Slightly Hard (96 PPM)

Slightly Hard (83 PPM)

Prioritize cities with multiple ZIPs and systems, then use source badges on each city page to separate verified treated-water records from estimates.

Top 10 Hardest Water Cities

#	City	Hardness
1	Coupeville	Very Hard (289 PPM)
2	Greenbank	Very Hard (289 PPM)
3	Oak Harbor	Very Hard (289 PPM)
4	Lopez	Very Hard (286 PPM)
5	Langley	Very Hard (283 PPM)
6	Clinton	Very Hard (278 PPM)
7	Brewster	Very Hard (257 PPM)
8	Malott	Very Hard (257 PPM)
9	Methow	Very Hard (257 PPM)
10	Okanogan	Very Hard (257 PPM)

Top 10 Softest Water Cities

#	City	Hardness
1	Arlington	Soft (12 PPM)
2	Brier	Soft (12 PPM)
3	Edmonds	Soft (12 PPM)
4	Everett	Soft (12 PPM)
5	Index	Soft (12 PPM)
6	Lake Stevens	Soft (12 PPM)
7	Lynnwood	Soft (12 PPM)
8	Marysville	Soft (12 PPM)
9	Mill Creek	Soft (12 PPM)
10	Mountlake Terrac	Soft (12 PPM)

All Cities in Washington

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

AberdeenSoft AcmeSoft AddySlightly Hard Airway HeightsHard AlbionModerately Hard AlgonaSoft AllynSoft AlmiraModerately Hard Amanda ParkSoft AmboySlightly Hard AnacortesSoft AnatoneSlightly Hard Anderson IslandSoft AppletonSlightly Hard ArdenvoirSlightly Hard ArielSlightly Hard ArlingtonSoft AshfordSoft AsotinSlightly Hard AuburnSoft Bainbridge IslanSlightly Hard BaringSoft Battle GroundSlightly Hard Bay CenterSlightly Hard Bear CreekSoft Beaux ArtsSoft BeaverModerately Hard BellevueSoft BellinghamSoft BengeHard Benton CityHard BeverlyHard BickletonHard Black DiamondSoft BlaineSoft Blakely IslandSoft Bonney LakeSoft BothellSoft BowSoft BremertonSlightly Hard BrewsterVery Hard BridgeportSlightly Hard BrierSoft BrinnonModerately Hard Brush PrairieSlightly Hard BuckleySoft BucodaSlightly Hard BurbankSoft BurienSoft BurlingtonSoft CamasSlightly Hard CarbonadoSoft CarltonHard CarnationSoft CarsonSoft Cascade ParkSlightly Hard CashmereSlightly Hard Castle RockSlightly Hard CathlametSoft CentervilleSlightly Hard CentraliaSoft ChattaroyHard ChehalisSoft ChelanSlightly Hard Chelan FallsSlightly Hard CheneyHard ChewelahSlightly Hard ChimacumModerately Hard ChinookSoft CinebarSoft Clallam BayModerately Hard ClarkstonSlightly Hard ClaytonSlightly Hard Cle ElumSlightly Hard ClearlakeSoft ClintonVery Hard ColbertHard ColfaxModerately Hard College PlaceSlightly Hard ColtonModerately Hard ColvilleSlightly Hard ConconullySlightly Hard ConcreteSoft ConnellModerately Hard ConwaySoft CookSoft Copalis BeachSoft Copalis CrossingSoft CosmopolisSoft CougarSlightly Hard Coulee CityHard Coulee DamSlightly Hard CoupevilleVery Hard CowicheSlightly Hard CrestonSlightly Hard CurlewModerately Hard CurtisSoft CusickSlightly Hard CusterSoft DallesportSlightly Hard DanvilleHard DarringtonSoft DavenportModerately Hard DaytonModerately Hard Deer HarborSlightly Hard Deer ParkHard Des MoinesSoft DixieSoft DotySoft DrydenSlightly Hard Du PontSoft DuvallSoft East WenatcheeSlightly Hard EastonSlightly Hard EastsoundSlightly Hard EatonvilleSoft EdmondsSoft EdwallSlightly Hard ElbeSoft Electric CityHard ElkHard EllensburgSlightly Hard ElmaSoft Elmer CitySlightly Hard EltopiaHard EndicottModerately Hard EntiatSlightly Hard EnumclawSoft EphrataHard EspanolaHard EthelSoft EvansSlightly Hard EverettSoft EversonSoft Fairchild Air FoHard FairfieldHard Fall CitySoft Federal WaySoft FelidaSlightly Hard FerndaleSoft FifeSoft FircrestSoft FordSlightly Hard ForksModerately Hard Fort LewisSoft Fox IslandSoft FreelandHard Friday HarborModerately Hard FruitlandSlightly Hard GarfieldModerately Hard GiffordSlightly Hard Gig HarborSoft GlacierSoft GlenomaSoft GlenwoodSlightly Hard Gold BarSoft GoldendaleHard GrahamSoft Grand CouleeHard GrandviewSlightly Hard GrangerSlightly Hard Granite FallsSoft GrapeviewSoft GraylandSoft Grays RiverSlightly Hard GreenbankVery Hard HansvilleSlightly Hard HarrahSlightly Hard HarringtonSlightly Hard HartlineHard HayModerately Hard Hazel DellSlightly Hard HobartSoft HomeSoft HoodsportSoft HoquiamSoft HumptulipsSoft HuntersSlightly Hard IlwacoSoft IncheliumHard IndexSoft IndianolaSlightly Hard IoneSlightly Hard IssaquahSoft KahlotusModerately Hard KalamaSlightly Hard KellerHard KelsoSlightly Hard KenmoreSoft KennewickHard KentSoft Kettle FallsSlightly Hard KeyportSlightly Hard KingstonSlightly Hard KirklandSoft KittitasSlightly Hard KlickitatSlightly Hard La CenterSlightly Hard La ConnerSoft La PushModerately Hard LaceySlightly Hard LacrosseModerately Hard Lake StevensSoft Lakewood CenterSoft LamontModerately Hard LangleyVery Hard LatahHard LaurierHard LeavenworthSoft Liberty LakeHard LilliwaupSoft LindModerately Hard Lk Forest ParkSoft Long BeachSoft LongbranchSoft LongviewSlightly Hard LoomisSlightly Hard Loon LakeModerately Hard LopezVery Hard LowdenSoft Lummi IslandSoft LyleSlightly Hard LyndenSoft LynnwoodSoft MabtonSlightly Hard MalagaSlightly Hard MaldenModerately Hard MaloHard MaloneSoft MalottVery Hard ManchesterSlightly Hard MansfieldSlightly Hard MansonSlightly Hard Maple ValleySoft MarblemountSoft MarcusSlightly Hard MarlinHard MarshallHard MarysvilleSoft MatlockSoft MattawaHard MazamaSlightly Hard Mc ClearySoft MeadHard MedinaSoft Mercer IslandSoft MesaHard MetalineSlightly Hard Metaline FallsHard MethowVery Hard MicaHard Mill CreekSoft MiltonSoft MineralSoft MoclipsSoft MohlerSlightly Hard MonitorSlightly Hard MonroeSoft MontesanoSoft MortonSoft Moses LakeHard MossyrockSoft Mount VernonSoft Mountlake TerracSoft MoxeeSlightly Hard MukilteoSoft NapavineSoft NaselleSlightly Hard Neah BayModerately Hard NespelemModerately Hard Newman LakeHard NewportModerately Hard Nine Mile FallsSlightly Hard NordlandModerately Hard Normandy ParkSoft North BendSoft North BonnevilleSlightly Hard NorthportSlightly Hard Oak HarborVery Hard OakesdaleModerately Hard OakvilleSoft Ocean CitySoft Ocean ParkSoft OdessaSlightly Hard OkanoganVery Hard OlallaSlightly Hard OlgaSoft OlympiaSlightly Hard OmakVery Hard OnalaskaSoft OrcasSoft OrchardsSlightly Hard OrientHard OrondoSlightly Hard OrovilleModerately Hard OrtingSoft Otis OrchardsHard OutlookSlightly Hard OystervilleSoft PacificSoft Pacific BeachSoft PackwoodSoft PalisadesSlightly Hard PalouseModerately Hard ParklandSoft PascoHard PaterosVery Hard PatersonHard Pe EllSoft PeshastinSlightly Hard PlymouthHard Point RobertsSoft PomeroySlightly Hard Port AngelesModerately Hard Port GambleSlightly Hard Port HadlockModerately Hard Port LudlowModerately Hard Port TownsendModerately Hard PoulsboSlightly Hard PrescottSoft ProsserHard PullmanModerately Hard PuyallupSoft QuilceneModerately Hard QuinaultSoft QuincyHard RainierSlightly Hard RandleSoft RavensdaleSoft RaymondSoft ReardanModerately Hard RedmondSoft RentonSoft RepublicModerately Hard RiceSlightly Hard RichlandHard RidgefieldSlightly Hard RitzvilleSlightly Hard RiversideVery Hard RochesterSlightly Hard Rock IslandSlightly Hard RockfordHard RockportSoft RonaldSlightly Hard RooseveltHard RosaliaModerately Hard RosburgSlightly Hard RoslynSlightly Hard RoySoft Royal CityHard RyderwoodSlightly Hard Saint JohnModerately Hard SalkumSoft SammamishSoft SeabeckSlightly Hard SeattleSoft SeaviewSlightly Hard Sedro WoolleySoft SekiuModerately Hard SelahSlightly Hard SequimHard Shaw IslandSoft SheltonSoft Silver CreekSoft SilverdaleSlightly Hard SilverlakeSlightly Hard SkamokawaSlightly Hard SkykomishSoft SnohomishSoft SnoqualmieSoft Snoqualmie PassSlightly Hard Soap LakeHard South BendSoft South Cle ElumSlightly Hard South Park VillaSlightly Hard South PrairieSoft SpanawaySoft SpangleHard SpokaneHard Spokane ValleyHard SpragueSlightly Hard SpringdaleSlightly Hard StanwoodSoft StarbuckModerately Hard StehekinSlightly Hard SteilacoomSoft StevensonSoft StratfordHard SultanSoft SumasSoft SunnysideSlightly Hard SuquamishSlightly Hard TacomaSoft TaholahSoft TahuyaSoft TekoaModerately Hard TeninoSlightly Hard Terrace HeightsSlightly Hard ThorntonModerately Hard ThorpSlightly Hard TietonSlightly Hard TokelandSlightly Hard ToledoSoft TonasketModerately Hard ToppenishSlightly Hard ToutleSlightly Hard Trout LakeSlightly Hard TukwilaSoft TumtumSlightly Hard TwispVery Hard UnderwoodSlightly Hard UnionSoft Union GapSlightly Hard UniontownModerately Hard UskHard VaderSoft ValleySlightly Hard ValleyfordHard VancouverSlightly Hard VantageSlightly Hard VashonSoft VaughnSoft WahkiacusSlightly Hard WaitsburgSlightly Hard WaldronSoft WallulaSoft WapatoSlightly Hard WardenHard WashougalSlightly Hard WashtucnaSlightly Hard WatervilleSlightly Hard WaucondaSoft WellpinitSlightly Hard WenatcheeSlightly Hard WestportSoft White PassSlightly Hard White SalmonSlightly Hard White SwanSlightly Hard Wide HollowSlightly Hard WilburModerately Hard WilkesonSoft Wilson CreekHard WinlockSoft WinthropVery Hard WishramSlightly Hard WoodinvilleSoft WoodlandSlightly Hard WoodwaySoft YacoltSlightly Hard YakimaSlightly Hard YelmSlightly Hard ZillahSlightly Hard