Hard Water Map

New Hampshire Water Hardness by County

Water in New Hampshire has a median hardness of 22.9 mg/L as CaCO₃ — "soft" on the USGS scale — based on 4,951 measurements at 2,284 monitoring stations. Rockingham County has the state's hardest measured water (62.9 mg/L); Carroll County the softest (12.7). Rank: #47 of the 50 states and D.C.

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

Of New Hampshire's 10 measured counties, 1 moderately hard and 9 soft. The hardest are Rockingham County (62.9 mg/L), Belknap County (51.8), and Sullivan County (24.4). Carroll County is the softest at 12.7 mg/L (soft).

No measured New Hampshire county reaches the hard threshold, so effectively none of its residents in counties with gate-passing hardness data live in a hard-or-worse county.

Statewide, New Hampshire's median works out to 1.3 grains per gallon and ranks #47 of the 50 states and D.C. Across 4,951 measurements at 2,284 stations — 1,953 of them since 2000 — the middle 80% of readings fall between 7.8 and 98 mg/L. The public record runs from 1952 to 2025.

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

Download the New Hampshire water hardness map (PNG) — Water hardness by county in New Hampshire: 10 counties mapped from USGS/EPA data, statewide median 22.9 mg/L (soft); darker counties have harder water.

By county

Water hardness by county

The table lists all 10 measured New Hampshire counties, hardest first. Their medians span 62.9 mg/L in Rockingham County to 12.7 in Carroll County — a 5× range.

County water hardness, hardest first — median mg/L as CaCO₃.
CountyMedianBandResultsSitesNewest
Rockingham County62.9Moderately hard5122262022
Belknap County51.8Soft2211692021
Sullivan County24.4Soft176862025
Grafton County22.5Soft6983492025
Strafford County22Soft3691422022
Hillsborough County19.1Soft6622342022
Cheshire County18.9Soft5141312024
Merrimack County18.8Soft8254562022
Coos County18.3Soft5492342024
Carroll County12.7Soft4252572021

ZIP codes

ZIP codes in New Hampshire

The ZIP codes below are grouped by the New Hampshire 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.

Rockingham County · 62.9 mg/L · Moderately hard

03032†03034†03036†03037†03038†03042†03044†03053†030770307903087†03261†03290†03291†0380103811†03819†03826†03827†0383303840†038410384203844†03848†0385403856†0385703858†03862†038650387003871†03873†0387403885†

Belknap County · 51.8 mg/L · Soft

03218†03220†03225†03226†03237†0324603249†03253†03256†03269†0380903810†03837†

Sullivan County · 24.4 mg/L · Soft

03280†03284†03601†03603†03605†03607†03743†03745†03751†03752†03753†03770†03773†03781†03782†

Grafton County · 22.5 mg/L · Soft

03215†03217†03222†03223†03238†03240†03241†03245†03251†03262†03264†03266†03279†03282†03285†03293†03561†03574†03580†03585†03586†03740†03741†03748†03750†03755†03765†0376603768†03771†03774†03777†03779†03780†03784†03785†

Strafford County · 22 mg/L · Soft

0382003823†03824†03825†03835†0383903851†03852†03855†03861†038670386803869†03878†03884†03887†

Hillsborough County · 19.1 mg/L · Soft

03031†03033†03043†03045†03047†03048†03049†03051†030520305403055†03057†0306003062030630306403070†03071†0307603082†03084†03086†0310103102031030310403109†03110†0324403281†03440†03442†03449†03458

Cheshire County · 18.9 mg/L · Soft

03431†03441†03443†03444†03445†03446†03447†03448†03450†03451†0345203455†03456†03457†0346103462†03464†0346503466†03467†03470†03602†03604†03608†03609†

Merrimack County · 18.8 mg/L · Soft

03046†0310603216†03221†03224†03229†03230†03231†03233†03234†03235†03242†03243†03255†0325703258†03260†03263†03268†03273†03275†03276†03278†03287†03301†03303†03304†03307†

Coos County · 18.3 mg/L · Soft

03570†03575†03576†03581†03582†03583†03584†03588†03590†03592†03593†03595†03597†03598†

Carroll County · 12.7 mg/L · Soft

03227†03254†03259†03812†03813†03814†03816†03817†03818†03830†03832†03836†03838†03845†03846†0384703849†03850†03853†0386003864†03872†03875†03882†03883†03886†03890†03894†03897†

† 208 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

New Hampshire's groundwater measures harder than its surface water — 58 mg/L across 1,936 samples versus 15 across 3,015, about 3.9× harder. Wells draw from groundwater, so well owners in New Hampshire tend to see the harder number — 58 mg/L, soft. Groundwater readings there run 15.2 to 147 mg/L across the middle 80% of samples. The comparison draws on 1,600 groundwater and 684 surface-water monitoring sites.

Groundwater (wells)

58 mg/L as CaCO₃ · 1,936 results at 1,600 stations.

Surface water (rivers, lakes)

15 mg/L as CaCO₃ · 3,015 results at 684 stations.

Groundwater measures about 3.9× harder than surface water here.

Chemistry

Water chemistry in New Hampshire

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

TDS

233 mg/L · n=331

233 mg/L — about 1× the national county median of 226, consistent with hard, mineral-rich water.

pH

6.5 pH · n=3,814

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

Alkalinity

43.8 mg/L as CaCO3 · n=507

43.8 mg/L — modest buffering capacity.

Calcium : Magnesium

5.4 : 1.2 mg/L ≈ 4.5 : 1 · n=1,394

Calcium is about 73% of New Hampshire's hardness (5.4 mg/L Ca to 1.2 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 New Hampshire

Two aquifer systems supply much of New Hampshire's measured groundwater.

  • New York and New England crystalline-rock aquifers — median 121 mg/L across 135 samples at 45 sites: hard.
  • Sand and gravel aquifers (glaciated regions) — median 36.9 mg/L across 480 samples at 382 sites: soft.

Together these systems account for 615 measured samples at 427 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

1950s2020s54

New Hampshire's decade median moved from 13 mg/L in the 1950s to 18 in the 2020s. Over the series, the decade median peaked at 54 mg/L in the 1980s and bottomed at 13 in the 1950s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.

Scale

Where New Hampshire sits on the scale

On the USGS scale, New Hampshire's 22.9 mg/L is soft — 1.3 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 gpg22.9 mg/L — Soft
Harder than 12% of the 2,977 measured county medians.

Questions

Frequently asked questions

Is New Hampshire's water hard?
New Hampshire's median hardness is 22.9 mg/L as CaCO₃, "soft" on the USGS scale and below the national county median of 140 mg/L.
Which county in New Hampshire has the hardest water?
Rockingham County, with a median of 62.9 mg/L as CaCO₃ across 512 measurements.
Is well water harder than city water in New Hampshire?
Groundwater measures harder here — about 3.9× the surface water — so wells tend to run harder (groundwater 58 vs surface water 15 mg/L).
How do I find my exact hardness in New Hampshire?
Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
Is New Hampshire's water harder than the national average?
No. New Hampshire's median of 22.9 mg/L is below the national county median of 140 mg/L; it ranks #47 of the 50 states and D.C.

Compare

States with similar hardness

Two states measure closest to New Hampshire's 22.9 mg/L: Georgia at 24.4 mg/L and Mississippi at 21.1 mg/L. New Hampshire measures harder than 8% 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 — 4,951 New Hampshire measurements. Data last verified . Methodology.

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