Hard Water Map

Connecticut Water Hardness by County

Water in Connecticut has a median hardness of 42.9 mg/L as CaCO₃ — "soft" on the USGS scale — based on 19,533 measurements at 2,571 monitoring stations. Fairfield County has the state's hardest measured water (86.8 mg/L); Windham County the softest (24.8). Rank: #40 of the 50 states and D.C.

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

Of Connecticut's 8 measured counties, 2 moderately hard and 6 soft. The hardest are Fairfield County (86.8 mg/L), New Haven County (76), and Litchfield County (49). Windham County is the softest at 24.8 mg/L (soft).

Population shares by hardness are not available for Connecticut.

Statewide, Connecticut's median works out to 2.5 grains per gallon and ranks #40 of the 50 states and D.C. Across 19,533 measurements at 2,571 stations — 5,907 of them since 2000 — the middle 80% of readings fall between 18 and 128 mg/L. The public record runs from 1915 to 2023.

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

Download the Connecticut water hardness map (PNG) — Water hardness by county in Connecticut: 8 counties mapped from USGS/EPA data, statewide median 42.9 mg/L (soft); darker counties have harder water.

By county

Water hardness by county

The table lists all 8 measured Connecticut counties, hardest first. Their medians span 86.8 mg/L in Fairfield County to 24.8 in Windham County — a 3.5× range.

County water hardness, hardest first — median mg/L as CaCO₃.
CountyMedianBandResultsSitesNewest
Fairfield County86.8Moderately hard2,5083322023
New Haven County76Moderately hard3,7483392023
Litchfield County49Soft2,0584072023
Hartford County41Soft4,9085572023
Middlesex County32Soft1,2821342023
New London County26Soft1,6103772023
Tolland County25Soft9901802023
Windham County24.8Soft2,4292452023

ZIP codes

ZIP codes in Connecticut

The ZIP codes below are grouped by the Connecticut county they fall in. Each ZIP takes its 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.

Fairfield County · 86.8 mg/L · Moderately hard

0646806470†06482†06484066040660506606066070660806610†0661106612†066140661506784†068010680406807068100681106812†0682006824068250683006831†0684006850068510685306854068550687006877068780688006883†0689006896†06897†069010690206903†069050690606907

New Haven County · 76 mg/L · Moderately hard

064010640306405064100641806437†06443†0645006451064600646106471†06472†064730647706478064830648806492†0651006511065120651306514065150651606517065180651906524†065250670206704067050670606708067100671206716†0676206770

Litchfield County · 49 mg/L · Soft

06018†06021†06024†06031†06039†06057†06058†0606106063†06068†06069†06079†06098†06750†06751†06752†06753†06754†06755†06756†06757†06758†06759†06763†06776†06777†06778†0677906782†06783†06785†067860678706790†06791†06793†06794†06795†06796†06798†

Hartford County · 41 mg/L · Soft

06001060020601006013†06016†06019†06020†06022†0602306026†06027†0603206033†06035†06037060400604206051060520605306059†06060†0606206065†060670607006073†060740607806080†06081060820608506088†0608906090†06091†0609206093†06095060960610306105061060610706108061090611006111061120611406117061180611906120†06444064470646706479†06489

Middlesex County · 32 mg/L · Soft

0640906412†06413†06414†0641606417†06419†06422†06423†06424†0642606438†06441†0644206455†06456†064570645906469†064750648006481†06498†

New London County · 26 mg/L · Soft

06249†06254†0632006330†06333†06334†0633506336†06338†06339†0634006350†06351†06353†063550635706359†0636006365†06370†06371†06375†0637606378†063790638006382†06384†06385†0638906415†06420†06439†

Tolland County · 25 mg/L · Soft

0602906043†06066060710607206076†06084†06231†06232†06237†06238†06248†06250†062680626906279†

Windham County · 24.8 mg/L · Soft

0622606234†06235†06239†06241†06242†06243†06247†0625506256†0625806259†06260†062620626306264†0626606277†06278†06280†06281†06282†06331†0633206354†06373†0637406377†06387

† 142 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

Connecticut's groundwater measures harder than its surface water — 75 mg/L across 2,232 samples versus 41.5 across 16,711, about 1.8× harder. Wells draw from groundwater, so well owners in Connecticut tend to see the harder number — 75 mg/L, moderately hard. Groundwater readings there run 25 to 200 mg/L across the middle 80% of samples. The comparison draws on 1,713 groundwater and 813 surface-water monitoring sites; 351 readings above 2,000 mg/L were logged but held out of the medians as outliers.

Groundwater (wells)

75 mg/L as CaCO₃ · 2,232 results at 1,713 stations.

Surface water (rivers, lakes)

41.5 mg/L as CaCO₃ · 16,711 results at 813 stations.

Groundwater measures about 1.8× harder than surface water here.

Chemistry

Water chemistry in Connecticut

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

TDS

149 mg/L · n=6,292

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

pH

7.6 pH · n=7,219

pH 7.6 — within the EPA secondary range of 6.5–8.5, on the alkaline side.

Alkalinity

29.3 mg/L as CaCO3 · n=8,205

29.3 mg/L — modest buffering capacity.

Calcium : Magnesium

13.4 : 3.3 mg/L ≈ 4.06 : 1 · n=6,133

Calcium is about 71% of Connecticut's hardness (13.4 mg/L Ca to 3.3 mg/L Mg), a little more calcium-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 Connecticut

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

  • New York and New England carbonate-rock aquifers — median 190 mg/L across 51 samples at 47 sites: very hard.
  • Early Mesozoic basin aquifers — median 110 mg/L across 270 samples at 268 sites: moderately hard.
  • Sand and gravel aquifers (glaciated regions) — median 78.8 mg/L across 1,253 samples at 784 sites: moderately hard.

Together these systems account for 1,574 measured samples at 1,099 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

1950s2020s52

Connecticut's decade median moved from 32 mg/L in the 1950s to 50.7 in the 2020s. Over the series, the decade median peaked at 51.7 mg/L in the 2010s and bottomed at 32 in the 1950s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.

Scale

Where Connecticut sits on the scale

On the USGS scale, Connecticut's 42.9 mg/L is soft — 2.5 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 gpg42.9 mg/L — Soft
Harder than 23% of the 2,977 measured county medians.

Questions

Frequently asked questions

Is Connecticut's water hard?
Connecticut's median hardness is 42.9 mg/L as CaCO₃, "soft" on the USGS scale and below the national county median of 140 mg/L.
Which county in Connecticut has the hardest water?
Fairfield County, with a median of 86.8 mg/L as CaCO₃ across 2,508 measurements.
Is well water harder than city water in Connecticut?
Groundwater measures harder here — about 1.8× the surface water — so wells tend to run harder (groundwater 75 vs surface water 41.5 mg/L).
How do I find my exact hardness in Connecticut?
Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
Is Connecticut's water harder than the national average?
No. Connecticut's median of 42.9 mg/L is below the national county median of 140 mg/L; it ranks #40 of the 50 states and D.C.

Compare

States with similar hardness

Two states measure closest to Connecticut's 42.9 mg/L: Massachusetts at 43.7 mg/L and Virginia at 42 mg/L. Connecticut measures harder than 22% 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 — 19,533 Connecticut measurements. Data last verified . Methodology.

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