Hard Water Map

Maryland Water Hardness by County

Water in Maryland has a median hardness of 58 mg/L as CaCO₃ — "soft" on the USGS scale — based on 14,908 measurements at 4,673 monitoring stations. Washington County has the state's hardest measured water (165 mg/L); Charles County the softest (12.4). Rank: #35 of the 50 states and D.C.

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

Of Maryland's 24 measured counties, 3 hard, 9 moderately hard, and 12 soft. The hardest are Washington County (165 mg/L), Baltimore County (132), and Calvert County (131). Charles County is the softest at 12.4 mg/L (soft).

About 18% of Maryland's roughly 6.2 million residents in counties with gate-passing hardness data live where tap water is hard or worse.

Statewide, Maryland's median works out to 3.4 grains per gallon and ranks #35 of the 50 states and D.C. Across 14,908 measurements at 4,673 stations — 4,736 of them since 2000 — the middle 80% of readings fall between 6.5 and 209 mg/L. The public record runs from 1906 to 2025.

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

Download the Maryland water hardness map (PNG) — Water hardness by county in Maryland: 24 counties mapped from USGS/EPA data, statewide median 58 mg/L (soft); darker counties have harder water.

By county

Water hardness by county

The table lists all 24 measured Maryland counties, hardest first. Their medians span 165 mg/L in Washington County to 12.4 in Charles County — a 13.3× range.

County water hardness, hardest first — median mg/L as CaCO₃.
CountyMedianBandResultsSitesNewest
Washington County165Hard1,5262712022
Baltimore County132Hard7643992019
Calvert County131Hard2531122016
Allegany County110Moderately hard593722022
Baltimore County91.4Moderately hard117972000
Cecil County88Moderately hard5271432024
Worcester County76Moderately hard5901952023
Harford County72.6Moderately hard9322522023
Prince George's County71Moderately hard3871232016
Queen Anne's County62.3Moderately hard3531632023
Garrett County61.8Moderately hard7882282023
Talbot County61Moderately hard88692023
Kent County57.6Soft8092062023
Carroll County51.6Soft4632062022
Somerset County47.2Soft1421182023
Montgomery County43Soft3121182022
Howard County40.3Soft2751482019
Anne Arundel County40Soft7674192023
Caroline County38Soft5211172023
Dorchester County37.2Soft4931382025
St. Mary's County28.5Soft2931322022
Frederick County28Soft3,1066162022
Wicomico County20Soft3451472023
Charles County12.4Soft4641842022

ZIP codes

ZIP codes in Maryland

The ZIP codes below are grouped by the Maryland 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.

Washington County · 165 mg/L · Hard

21711†21713†21715†2171921722†21733†217342174021742†21746†21750†21756†2176721779†21781†2178221783†21795†

Baltimore County · 132 mg/L · Hard

21013†21023†210302103121051†2105221053†21057†21071†21082†21087†2109321105†21111†2111721120†2112821131†2113321136†21152†21153†21155†21156†2116221163†21204212072120821209212192122021221†21222212272122821234212362123721244†21250212522128521286

Calvert County · 131 mg/L · Hard

20615†2062920639†20657†20676†20678†20685†2068820689†20732†20736†20754†

Allegany County · 110 mg/L · Moderately hard

2150221524†21529†21530†21532†2154021542†21543†2154521555†21557†21560†21766†

Baltimore County · 91.4 mg/L · Moderately hard

212012120221205212062121021211212122121321214212152121621217212182122321224212262122921230†2123121233212392125121287

Cecil County · 88 mg/L · Moderately hard

21901†2190221903†21904†21911†21912†21913†2191421915†21917†21918†21919†21920†2192121930†

Worcester County · 76 mg/L · Moderately hard

2181121813†21829†21841†21842†21851†21862†21863†21864†21872†

Harford County · 72.6 mg/L · Moderately hard

21001†210052100921010†2101421015†2101721028†21034†2104021047†21050†21078†21084†21085†21130†21132†21154†21160†21161†

Prince George's County · 71 mg/L · Moderately hard

2060720608†20613†206232070520706207072070820710207122071520716†207202072120722207352073720740207422074320744207452074620747207482076220769207702077120772†207742078120782207832078420785

Queen Anne's County · 62.3 mg/L · Moderately hard

21607†21617†21619†21623†2162821638†21644†21649†21657†21658†21666†21668

Garrett County · 61.8 mg/L · Moderately hard

21520†21521†21523†21531†21536†21538†21539†215412155021561†21562†

Talbot County · 61 mg/L · Moderately hard

2160121612†21624†21625†21647†21652†21653†21654†21662†21663†21665†21671†21673†21676†21679†

Kent County · 57.6 mg/L · Soft

2161021620†21635†21645†21650†21651†21661†21667†21678†

Carroll County · 51.6 mg/L · Soft

21048†21074†21102†21157†21158†21757†21776†21784†21787†

Somerset County · 47.2 mg/L · Soft

2181721821†21824†21838†2185321866†21867†21871†21890

Montgomery County · 43 mg/L · Soft

20812†20814208152081620817208182083220833†20837†20838†20839†20841†20842†208502085120852208532085420855208602086120862†208662086820871†2087220874†208762087720878208792088020882†208862088920892208942089520896208992090120902209032090420905209062091020912

Howard County · 40.3 mg/L · Soft

2070120723†20759†2076320777†20794†21029†21036†21042†210432104421045210462107521104†21723†21737†21738†21794†21797†

Anne Arundel County · 40 mg/L · Soft

20711†20714†20724†20733†20751†2075520758†20764†20765†20776†20778†20779†2101221032†21035†21037†2105421056210602106121076210772109021108211132111421122†2114021144211462122521240214012140221403†21405†21409

Caroline County · 38 mg/L · Soft

21629†21632†21636†21639†21640†21641†21655†21660

Dorchester County · 37.2 mg/L · Soft

21613†21622†21626†21627†21631†21634†21643†21648†21659†2166421669†21672†21675†21677†21835†21869†

St. Mary's County · 28.5 mg/L · Soft

20606†20609†20618†20619†20620†20621†20624†20626†20628†20630†2063420636†20650†20653†20656†20659†20660†20667†2067020674†20680†20684†20686†20687†2069020692†

Frederick County · 28 mg/L · Soft

21701†21702†21703†21704†2170521710†21714†2171621717†21718†21727†21754†21755†21758†21762†21769†21770†21771†21773†21774†2177721778†21780†21788†21790†21791†2179321798†

Wicomico County · 20 mg/L · Soft

21801†21804†21810†21814†218222182621830†21837†21840†21849†21850†21856†21861†21865†2187421875†

Charles County · 12.4 mg/L · Soft

20601†20602†2060320611†20612†20616†20617†20622†20625†20632†20637†20640†20645†20646†20658†20661†20662†20664†20675†20677†20693†20695†

† 294 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

Maryland's groundwater measures harder than its surface water — 62 mg/L across 5,738 samples versus 58 across 8,876, about 1.1× harder. Wells draw from groundwater, so well owners in Maryland tend to see the harder number — 62 mg/L, moderately hard. Groundwater readings there run 8 to 269 mg/L across the middle 80% of samples. The comparison draws on 3,518 groundwater and 1,144 surface-water monitoring sites; 63 readings above 2,000 mg/L were logged but held out of the medians as outliers.

Groundwater (wells)

62 mg/L as CaCO₃ · 5,738 results at 3,518 stations.

Surface water (rivers, lakes)

58 mg/L as CaCO₃ · 8,876 results at 1,144 stations.

Groundwater measures about 1.1× harder than surface water here.

Chemistry

Water chemistry in Maryland

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

TDS

135 mg/L · n=3,102

135 mg/L — below the national county median of 226.

pH

7.4 pH · n=3,907

pH 7.4 — within the EPA secondary range of 6.5–8.5, on the alkaline side.

Alkalinity

45 mg/L as CaCO3 · n=5,421

45 mg/L — modest buffering capacity.

Calcium : Magnesium

20.3 : 6.8 mg/L ≈ 2.99 : 1 · n=4,874

Calcium is about 64% of Maryland's hardness (20.3 mg/L Ca to 6.8 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 Maryland

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

  • Alluvial aquifers — median 287 mg/L across 127 samples at 40 sites: very hard.
  • Valley and Ridge aquifers — median 230 mg/L across 274 samples at 231 sites: very hard.
  • Piedmont and Blue Ridge carbonate-rock aquifers — median 200 mg/L across 200 samples at 131 sites: very hard.

Together these systems account for 601 measured samples at 402 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

1940s2020s82

Maryland's decade median moved from 42.5 mg/L in the 1940s to 82 in the 2020s. Over the series, the decade median peaked at 82 mg/L in the 2020s and bottomed at 37.8 in the 1980s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.

Scale

Where Maryland sits on the scale

On the USGS scale, Maryland's 58 mg/L is soft — 3.4 grains per gallon, below the 60 mg/L soft cutoff — among the softest water measured in the US.

SoftModerately hardHardVery hard60 · 3.5 gpg120 · 7.0 gpg180 · 10.5 gpg58 mg/L — Soft
Harder than 28% of the 2,977 measured county medians.

Questions

Frequently asked questions

Is Maryland's water hard?
Maryland's median hardness is 58 mg/L as CaCO₃, "soft" on the USGS scale and below the national county median of 140 mg/L.
Which county in Maryland has the hardest water?
Washington County, with a median of 165 mg/L as CaCO₃ across 1,526 measurements.
Is well water harder than city water in Maryland?
Groundwater measures harder here — about 1.1× the surface water — so wells tend to run harder (groundwater 62 vs surface water 58 mg/L).
How do I find my exact hardness in Maryland?
Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
Is Maryland's water harder than the national average?
No. Maryland's median of 58 mg/L is below the national county median of 140 mg/L; it ranks #35 of the 50 states and D.C.

Compare

States with similar hardness

Two states measure closest to Maryland's 58 mg/L: New Jersey at 59.9 mg/L and Arkansas at 62 mg/L. Maryland measures harder than 32% 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 — 14,908 Maryland measurements. Data last verified . Methodology.

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