Hard Water Map

Ohio Water Hardness by County

Water in Ohio has a median hardness of 270 mg/L as CaCO₃ — "very hard" on the USGS scale — based on 93,580 measurements at 10,558 monitoring stations. Belmont County has the state's hardest measured water (374 mg/L); Carroll County the softest (120). Rank: #7 of the 50 states and D.C.

Ohio water hardness map — what the numbers mean. Data verified 2026-07-22.

Every one of Ohio's 88 measured counties tests hard or harder: 76 rank very hard and 12 rank hard. The hardest are Belmont County (374 mg/L), Clark County (367.5), and Champaign County (366.5). Even Carroll County, the softest measured area in the state, reads 120 mg/L — still hard on the USGS scale.

About 100% of Ohio's roughly 11.8 million residents in counties with gate-passing hardness data live where tap water is hard or worse.

Statewide, Ohio's median works out to 15.8 grains per gallon and ranks #7 of the 50 states and D.C. Across 93,580 measurements at 10,558 stations — 61,680 of them since 2000 — the middle 80% of readings fall between 131 and 422 mg/L. The public record runs from 1938 to 2024.

See where Ohio sits nationally on the national map, or what its number means on the hardness scale.

Download the Ohio water hardness map (PNG) — Water hardness by county in Ohio: 88 counties mapped from USGS/EPA data, statewide median 270 mg/L (very hard); darker counties have harder water.

By county

Water hardness by county

The table lists all 88 measured Ohio counties, hardest first. Their medians span 374 mg/L in Belmont County to 120 in Carroll County — a 3.1× range.

County water hardness, hardest first — median mg/L as CaCO₃.
CountyMedianBandResultsSitesNewest
Belmont County374Very hard1,2132062024
Clark County367.5Very hard1,0081302024
Champaign County366.5Very hard7401082020
Hardin County364Very hard496672024
Logan County361Very hard6691042024
Greene County360Very hard1,4441692024
Wyandot County356Very hard937732024
Mercer County355Very hard773892024
Darke County354Very hard1,3721712020
Madison County351Very hard8681092024
Shelby County351Very hard531912022
Harrison County350Very hard7981272024
Union County331Very hard1,3151402024
Auglaize County330Very hard8591062024
Huron County330Very hard783942024
Miami County330Very hard1,1891552024
Montgomery County328Very hard2,8973032024
Preble County328Very hard7591312024
Butler County326Very hard2,1952162021
Tuscarawas County322Very hard1,9592892024
Fayette County320Very hard633732024
Marion County313Very hard947842024
Seneca County313Very hard574532024
Hancock County312Very hard956972024
Sandusky County310Very hard1,1441102024
Allen County308Very hard1,4901502024
Fairfield County308Very hard1,3471292022
Perry County304Very hard5911722022
Putnam County304Very hard1,307802024
Pickaway County302.5Very hard1,8081242024
Crawford County302Very hard506632024
Hamilton County301Very hard1,9661462024
Stark County298Very hard1,9501882024
Fulton County296Very hard409442024
Warren County295Very hard692932024
Henry County293.5Very hard366422024
Noble County293Very hard412852016
Williams County291.5Very hard5461152024
Morrow County290Very hard802602024
Ottawa County288Very hard560532024
Van Wert County287Very hard351472024
Highland County282.5Very hard360592024
Ross County281Very hard1,582972024
Wood County280Very hard1,1431752024
Franklin County277Very hard3,3283702024
Morgan County275Very hard8331072024
Clinton County274Very hard325672018
Delaware County272Very hard1,7491102024
Columbiana County271Very hard1,1951462024
Defiance County270Very hard1,149592024
Licking County270Very hard914902024
Richland County269Very hard436622024
Paulding County267.5Very hard490512024
Erie County267Very hard907732024
Jefferson County260Very hard1,4191932024
Wayne County257Very hard7991272024
Muskingum County249.5Very hard1,0011632024
Medina County246Very hard503722018
Ashland County240Very hard509522024
Athens County238Very hard1,6731972024
Lucas County236Very hard2,6761662024
Lorain County230Very hard1,8551402024
Holmes County225Very hard606832024
Summit County221.5Very hard2,0772022024
Hocking County221Very hard8101182024
Knox County221Very hard874542024
Cuyahoga County216Very hard3,1472022024
Guernsey County214Very hard9621432024
Clermont County211.5Very hard1,2161272024
Adams County210Very hard228572019
Coshocton County198Very hard1,3651962024
Jackson County196Very hard326612024
Mahoning County192Very hard1,5261212024
Brown County190Very hard425742024
Washington County189.5Very hard1,0761762024
Portage County180Very hard9521532024
Pike County179Hard4581132024
Lake County178Hard1,228722024
Geauga County168Hard8041652024
Gallia County160Hard9651082024
Monroe County151Hard444782018
Meigs County150Hard306642019
Scioto County150Hard1,275932022
Trumbull County150Hard1,4691342024
Vinton County150Hard1,3141262024
Lawrence County142Hard5691162019
Ashtabula County132Hard1,5691672024
Carroll County120Hard581932022

ZIP codes

ZIP codes in Ohio

The ZIP codes below are grouped by the Ohio county each mostly falls within (by land area). Each ZIP takes that county's measured median — shown in the group header — so this is a ZIP-to-county guide, not a separate reading for every ZIP. To check the water system serving a specific address, use the lookup.

Key: a † after a ZIP means it has no mapped community water system — usually a private-well area. Plain ZIPs are served by a mapped community water system.

Belmont County · 374 mg/L · Very hard

4371343718†43719†4375943902†43905†43906†43909†43912†43928†43933†4393443935†43940†43942†43947†43950†43951†43967†43972†43977†43983†43985

Clark County · 367.5 mg/L · Very hard

4301045316†45319†4532345341†45344†4534945368†45369†45372†45501455024550345504†45505†45506†

Champaign County · 366.5 mg/L · Very hard

43009†43044†43047†43060†43070†43072†43078†43084†45317†45389

Hardin County · 364 mg/L · Very hard

43310†4332643340†43346†45810†45812†45835†4583645843†45859

Logan County · 361 mg/L · Very hard

433114331843319†43324†43331†43333†43336†43343†43345†43347†4334843357†43360†

Greene County · 360 mg/L · Very hard

45301453054530745314†4532445335†4537045384†453854538745430454314543245433454344543545440

Wyandot County · 356 mg/L · Very hard

4331643323†43330†43351†43359†44849†44882†

Mercer County · 355 mg/L · Very hard

45310†45822†4582645828†45846†45860†4586245866†45882†45883†

Darke County · 354 mg/L · Very hard

45303†45304†45308†4532845331†45332†45346†45348†45350†45351†45352†45358†45362†45380†45388†45390†

Madison County · 351 mg/L · Very hard

43029†43064†43140†43143†4315143153†43162†

Shelby County · 351 mg/L · Very hard

45302†45306†45333†4533445336†45340†45353†45360†45363†4536545845†

Harrison County · 350 mg/L · Very hard

4390743973†4397443976†4398143986†43988†44693†44699†

Union County · 331 mg/L · Very hard

43007†43036†4304043045†43067†43077†43344†43358†

Auglaize County · 330 mg/L · Very hard

45819†4586545869†45870†45871†45884†45885†45888†45895†45896†

Huron County · 330 mg/L · Very hard

44811†44826†44837†44847†44850†44851†44855†44857†44865†44889†44890†

Miami County · 330 mg/L · Very hard

45312†4531845326†45337†45339†453564535945361†453714537345383†

Montgomery County · 328 mg/L · Very hard

453094531545322†45325†45327†453424534545354†45377†454024540345404454054540645409454104541445415454164541745419†45420†454234542445426454284542945439†45449454584545945469

Preble County · 328 mg/L · Very hard

45003†450704531145320†45321†453304533845347†453784538145382†

Butler County · 326 mg/L · Very hard

45011†4501345014450154504245044450504505345055†450564506245064†45067†45069

Tuscarawas County · 322 mg/L · Very hard

43832†43837†43840†44612†44621†4462244629†4465344656†4466344671†44678†44680†446814468244683†44697†

Fayette County · 320 mg/L · Very hard

43106†43128†43142†43160

Marion County · 313 mg/L · Very hard

433024331443322†43332†43337†43341†43342†43356

Seneca County · 313 mg/L · Very hard

44802†44807†44809†4481544818†44828†4483044836†44841†44844†44853†44861†44867†44883

Hancock County · 312 mg/L · Very hard

44804†45814†45816†4584045841†4585845867†45868†45881†45889†45890†45897†

Sandusky County · 310 mg/L · Very hard

43407†43410†4342043431†43435†4344243464†43469†

Allen County · 308 mg/L · Very hard

45801†45804†4580545806†45807†4580845809†45817†45820†458334585045854†45887†

Fairfield County · 308 mg/L · Very hard

4304643102†43105†43107†43110†4311243130431364314743148†43150†43154†43155†43157

Perry County · 304 mg/L · Very hard

43076†43730†43731†43739†43748†43760†43761†43764†43766†43782†43783†

Putnam County · 304 mg/L · Very hard

45815†45827†45830†45831†45844†458484585345856†45864†45875†4587645877†45893†

Pickaway County · 302.5 mg/L · Very hard

43103†43113†431164311743137†43145†43146†43156†43164

Crawford County · 302 mg/L · Very hard

4482044825†44827†44854†44856†44881†44887†

Hamilton County · 301 mg/L · Very hard

45001†450024503045033450414505145052451114517445202452034520445205452064520745208452094521145212452134521445215†4521645217452184521945220452234522445225452264522745229452304523145232452334523645237452384523945240452414524245243452444524645247452484524945251452524525545267

Stark County · 298 mg/L · Very hard

4460144608†446134461444626†4463044632†44640†44641†446464464744652†44662†44666†44669†44670†44688†447024470344704447054470644707†447084470944710447144471844720†44721†44730†

Fulton County · 296 mg/L · Very hard

43502†43515†43521†4353343540†4355343558†43567†

Warren County · 295 mg/L · Very hard

45005†45032†4503445036450394504045054†450654506645068†45152†45162

Henry County · 293.5 mg/L · Very hard

43510†43516†43523†4352443527†43532†43534†43535†4354543548†43555

Noble County · 293 mg/L · Very hard

43711†4371743724†43772†43779†43788†45727†45745†

Williams County · 291.5 mg/L · Very hard

43501†43505†4350643517†43518†43531†43543†43554†43557†43570

Morrow County · 290 mg/L · Very hard

4300343315433174332043321433254333443338†4335044833

Ottawa County · 288 mg/L · Very hard

43408†43416†43430†43432†43433†43436†4343943440†43445†43446†43449†43452†43456†43458†43468†

Van Wert County · 287 mg/L · Very hard

45832†45838†45863†45874†4589145894†45898†45899†

Highland County · 282.5 mg/L · Very hard

4512345132†45133†45135†45142†4515545172†

Ross County · 281 mg/L · Very hard

4310143115†45601†45612†4561745628456444567345681†

Wood County · 280 mg/L · Very hard

43402†4340343406†43413†43414†43437†434434344743450†43451†43457†43460†43462†434634346543466†43467†43511†43522†43525†43529†43541†4355143565435694361944817†45872

Franklin County · 277 mg/L · Very hard

4300243004430164301743026430544306843081430854310943119†4312343125431264320143202432034320443205432064320743209432104321143212432134321443215432174321843219432204322143222432234322443227432284322943230432314323243235

Morgan County · 275 mg/L · Very hard

4372843756†43758†43787†45715†

Clinton County · 274 mg/L · Very hard

451074511345146†45148†45159†45164†45166†45169†45177†

Delaware County · 272 mg/L · Very hard

430154302143032†43035430614306543066430744308243240

Columbiana County · 271 mg/L · Very hard

43920†43945†43962†43968†444084441344415†44423†44431†44432†44441†4444544455†444604449044493†44625†44634†44665†

Defiance County · 270 mg/L · Very hard

4351243519†43520†43526†43530†43536†43549†43556†

Licking County · 270 mg/L · Very hard

430014300843013†43018†4302343025†43027†43030†43031†4303343055†43056†4306243071†43080†43721†43740

Richland County · 269 mg/L · Very hard

44813†44822†44843†4487544878†44901449024490344904†44905†4490644907

Paulding County · 267.5 mg/L · Very hard

45813†45821†45849†45851†45855†45861†45873†45879†45880†45886†

Erie County · 267 mg/L · Very hard

43438†4408944814†44824448394484644870

Jefferson County · 260 mg/L · Very hard

43901†43908†43910†43913†43917†43925†43926†43930†43932†43938†43939†43943†43944439484395243953†43961439634396443971

Wayne County · 257 mg/L · Very hard

44214†44217†442304427044276†44287†44606†44618†44645†446594466744676†44677†44691†

Muskingum County · 249.5 mg/L · Very hard

4370143720†43727†4373443735†4373843746†43762†43767†43771†43777†4379143802†43821†43822†43830†43842

Medina County · 246 mg/L · Very hard

44212442154423344235442514425344254†4425644273†44274†442754428044281

Ashland County · 240 mg/L · Very hard

448054483844840†44842†4485944864†44866†4487444880

Athens County · 238 mg/L · Very hard

45701†45711†45716†4571945723†45732†45735†45739†45740†4576145766†45778†4578045782

Lucas County · 236 mg/L · Very hard

43412†4343443504†435284353743542†43547†43560†43566†43571436044360543606436074360843609436104361143612†4361343614436154361643617†4362043623

Lorain County · 230 mg/L · Very hard

44001†440114401244028440354403944044440494405044052†44053†44054440554407444090

Holmes County · 225 mg/L · Very hard

43804†4461044611†44624†44627†44628†44633†44637†44638†44654†44660†44661†4468744689†44690

Summit County · 221.5 mg/L · Very hard

4405644067440874420344216†4422144223442244423244236442504426244264†44278442864430144302443034430444305443064430744308443104431144312†443134431444319†4432044321†4432544333†44685†

Hocking County · 221 mg/L · Very hard

4311143127†43135†43138†43144†43149†43152†43158†45764†

Knox County · 221 mg/L · Very hard

43005†4301143014†43019†43022†43028†43037†43050†

Cuyahoga County · 216 mg/L · Very hard

4401744022†4404044070441014410244103441044410544106441074410844109441104411144112441134411444115441164411744118441194412044121441224412344124441254412644127441284412944130441314413244133441344413544136441374413844139441404414144142441434414444145441464414744149

Guernsey County · 214 mg/L · Very hard

43722†43723†4372543732†43733†43736†43749†43750†43755†43768†43773†43778†43780†

Clermont County · 211.5 mg/L · Very hard

451024510345106451124512045122†451404514745150451534515645157451584516045176†45245

Adams County · 210 mg/L · Very hard

4510545144†45616†4561845650†45660†45679†45684†4569345697†

Coshocton County · 198 mg/L · Very hard

43006†43805†43811†43812†43824†4383643843†43844†43845†

Jackson County · 196 mg/L · Very hard

4562145640†4565645685†45692

Mahoning County · 192 mg/L · Very hard

44401†4440544406†44429†4443644442†44443†44449†44451†4445244454†4447144502445034450444505445064450744509445104451144512445144451544555446094461944672

Brown County · 190 mg/L · Very hard

45101†45115†4511845119†4512145130†45131†4515445167†45168†45171†

Washington County · 189.5 mg/L · Very hard

45714†45721†4572445729†4574245744†45746†4575045767†45768†45773†4578445786†45788†45789†

Portage County · 180 mg/L · Very hard

44201†4420244231†44234†44240†44241442434425544260†44266†44272†44285†44288†44411†44412†

Pike County · 179 mg/L · Hard

4561345624†45642†45646†45661†45690†

Lake County · 178 mg/L · Hard

44045†44057†4406044077†44081440924409444095

Geauga County · 168 mg/L · Hard

44021†44023†4402444026†44046†44062†44064†44065†44072†44080†44086†

Gallia County · 160 mg/L · Hard

45614†45620†45623†4563145658†4567445686†

Monroe County · 151 mg/L · Hard

43716†43747†43754†43786†43793†43914†43915†4393143946†45734†

Meigs County · 150 mg/L · Hard

45710†45720†4574145743†4576045769†45770†45771†45772†4577545776†4577945783

Scioto County · 150 mg/L · Hard

45629†4563045636†45648†45652†45653†45657†45662†45663†45671†45677†45682†45694†45699†

Trumbull County · 150 mg/L · Hard

44402†4440344404†44410†44417†44418†44420†44424†4442544428†44430†4443744438†44439†44440†444444444644450†44470†444734448144483†44484†4448544491†

Vinton County · 150 mg/L · Hard

45622†45634†4564745651†45654†45672†45695†45698†

Lawrence County · 142 mg/L · Hard

4561945638456454565945669†45678†4568045688†45696†

Ashtabula County · 132 mg/L · Hard

44003†4400444010†44030†44032†44041†44047†44048†44068†44076†44082†44084†44085†44093†44099†

Carroll County · 120 mg/L · Hard

43903†44427†44607†44615†44620†44639†44643†4464444651†4465744675†44695†

† 690 ZIP codes are not served by a mapped community water system — most are private-well areas. See well water hardness.

Check any ZIP's utility and hardness →

Source

Groundwater vs surface water

Ohio's groundwater measures harder than its surface water — 360 mg/L across 4,174 samples versus 263 across 82,470, about 1.4× harder. Wells draw from groundwater, so well owners in Ohio tend to see the harder number — 360 mg/L, very hard. Groundwater readings there run 157.4 to 639 mg/L across the middle 80% of samples. The comparison draws on 1,764 groundwater and 7,964 surface-water monitoring sites; 313 readings above 2,000 mg/L were logged but held out of the medians as outliers.

Groundwater (wells)

360 mg/L as CaCO₃ · 4,174 results at 1,764 stations.

Surface water (rivers, lakes)

263 mg/L as CaCO₃ · 82,470 results at 7,964 stations.

Groundwater measures about 1.4× harder than surface water here.

Chemistry

Water chemistry in Ohio

Beyond the hardness number, Ohio's water carries a fuller chemical signature — here is how its measured parameters compare to national benchmarks.

TDS

396 mg/L · n=38,425

396 mg/L — about 1.8× the national county median of 226, consistent with hard, mineral-rich water.

pH

7.9 pH · n=24,131

pH 7.9 — within the EPA secondary range of 6.5–8.5, on the alkaline side.

Alkalinity

170 mg/L as CaCO3 · n=58,692

170 mg/L — substantial buffering capacity, which resists pH swings.

Calcium : Magnesium

69 : 21.4 mg/L ≈ 3.22 : 1 · n=62,051

Calcium is about 66% of Ohio's hardness (69 mg/L Ca to 21.4 mg/L Mg), a little more magnesium-rich than the national ~68% calcium share.

Parameter medians may include a small share of quality-control samples; the hardness lane is fully QC-filtered.

Aquifers

Major aquifers under Ohio

3 aquifer systems supply much of Ohio's measured groundwater.

  • Silurian-Devonian aquifers — median 451 mg/L across 335 samples at 286 sites: very hard.
  • Sand and gravel aquifers (glaciated regions) — median 375 mg/L across 1,673 samples at 708 sites: very hard.
  • Alluvial aquifers — median 264.5 mg/L across 60 samples at 35 sites: very hard.

Together these systems account for 2,068 measured samples at 1,029 sites. Aquifer medians pool samples across a whole system and can mask local variation — see the national aquifer map for how these compare across states.

Trend

Hardness over time

1950s2020s318

Ohio's decade median moved from 270 mg/L in the 1950s to 258 in the 2020s. Over the series, the decade median peaked at 318 mg/L in the 1990s and bottomed at 240 in the 2010s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.

Scale

Where Ohio sits on the scale

On the USGS scale, Ohio's 270 mg/L is very hard — 15.8 grains per gallon, well above the 180 mg/L very-hard cutoff — among the hardest water measured in the US.

SoftModerately hardHardVery hard60 · 3.5 gpg120 · 7.0 gpg180 · 10.5 gpg270 mg/L — Very hard
Harder than 77% of the 2,977 measured county medians.

At 270 mg/L (15.8 gpg), water-softener owners in Ohio typically set their unit to this hardness — settings calculator.

Questions

Frequently asked questions

Is Ohio's water hard?
Ohio's median hardness is 270 mg/L as CaCO₃, "very hard" on the USGS scale and 1.93× the national county median of 140 mg/L. About 100% of residents in measured counties have hard-or-worse water.
Which county in Ohio has the hardest water?
Belmont County, with a median of 374 mg/L as CaCO₃ across 1,213 measurements. Even the softest, Carroll County at 120 mg/L, is still "hard" on the USGS scale.
Is well water harder than city water in Ohio?
Groundwater measures harder here — about 1.4× the surface water — so wells tend to run harder (groundwater 360 vs surface water 263 mg/L).
How do I find my exact hardness in Ohio?
Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
Is Ohio's water harder than the national average?
Yes. Ohio's median of 270 mg/L is 1.93× the national county median of 140 mg/L, and Ohio ranks #7 of the 50 states and D.C.

Compare

States with similar hardness

Two states measure closest to Ohio's 270 mg/L: Utah at 270 mg/L and Indiana at 280 mg/L. Ohio measures harder than 88% of states. Browse the full ranking on the statistics page.

More: hardness scale · check your address · national statistics · the national map.

By . Source: USGS/EPA Water Quality Portal — 93,580 Ohio measurements. Data last verified . Methodology.

Cite this page: “Ohio Water Hardness by County.” Hard Water Map. Retrieved 2026-07-22, https://hardwatermap.com/water-hardness/ohio/