Maine Water Hardness by County
Water in Maine has a median hardness of 16.3 mg/L as CaCO₃ — "soft" on the USGS scale — based on 3,490 measurements at 940 monitoring stations. York County has the state's hardest measured water (53.5 mg/L); Oxford County the softest (6). Rank: #51 of the 50 states and D.C.
Maine water hardness map — what the numbers mean. Data verified 2026-07-22.
Of Maine's 14 measured counties, 14 soft. The hardest are York County (53.5 mg/L), Waldo County (50), and Aroostook County (44). Oxford County is the softest at 6 mg/L (soft).
No measured Maine 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, Maine's median works out to 1 grains per gallon and ranks #51 of the 50 states and D.C. Across 3,490 measurements at 940 stations — 1,065 of them since 2000 — the middle 80% of readings fall between 4.9 and 75 mg/L. The public record runs from 1941 to 2023.
See where Maine sits nationally on the national map, or what its number means on the hardness scale.
Download the Maine water hardness map (PNG) — Water hardness by county in Maine: 14 counties mapped from USGS/EPA data, statewide median 16.3 mg/L (soft); darker counties have harder water.
By county
Water hardness by county
The table lists all 14 measured Maine counties, hardest first. Their medians span 53.5 mg/L in York County to 6 in Oxford County — a 8.9× range. 2 more Maine counties lack gate-passing data.
| County | Median | Band | Results | Sites | Newest |
|---|---|---|---|---|---|
| York County | 53.5 | Soft | 105 | 78 | 2019 |
| Waldo County | 50 | Soft | 24 | 16 | 2011 |
| Aroostook County | 44 | Soft | 319 | 95 | 2009 |
| Knox County | 39 | Soft | 23 | 18 | 2007 |
| Franklin County | 29.7 | Soft | 49 | 39 | 2011 |
| Androscoggin County | 22 | Soft | 135 | 41 | 2023 |
| Kennebec County | 20 | Soft | 235 | 72 | 2011 |
| Penobscot County | 19 | Soft | 251 | 52 | 2011 |
| Cumberland County | 17.6 | Soft | 558 | 118 | 2019 |
| Somerset County | 15 | Soft | 166 | 56 | 2019 |
| Piscataquis County | 12.9 | Soft | 40 | 33 | 2014 |
| Hancock County | 11.6 | Soft | 391 | 66 | 2007 |
| Washington County | 11.3 | Soft | 290 | 65 | 2023 |
| Oxford County | 6 | Soft | 897 | 184 | 2023 |
ZIP codes
ZIP codes in Maine
The ZIP codes below are grouped by the Maine 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.
York County · 53.5 mg/L · Soft
03901†03902†03903†0390403905†03906†0390703908†03909†039100391104001†04002†040050400604020†04027†04030†04042†0404304046†04047†0404804049†04056†04061040630406404072†0407304076†0408304087†04090†04093†04095†
Waldo County · 50 mg/L · Soft
04354†04438†04496†04848†04849†04915†04921†04922†04941†04949†04951†04952†04973†04974†04981†04986†04987†04988†
Aroostook County · 44 mg/L · Soft
04451†04459†04471†04497†04730†04732†04733†04734†04735†04736†04737†04739†04740†04742†04743†04745†04746†04747†04750†04756†04757†04758†04760†04761†04762†04763†04764†04766†04768†0476904772†04773†04774†04776†04779†04780†04781†04783†04785†04786†04787†
Knox County · 39 mg/L · Soft
04547†04563†04574†04645†04841†04843†04847†04851†04853†04854†04855†04856†04858†04859†04860†04861†04862†04863†04864†
Franklin County · 29.7 mg/L · Soft
0423404239†04285†04294†04936†04938†04940†04947†04955†04956†04966†04970†04982†04983†04984†04992
Androscoggin County · 22 mg/L · Soft
0421004222†04236†04240†0425004252†04253†04254†04256†04258†04263†04274†04280†04282†
Kennebec County · 20 mg/L · Soft
04259†04265†04284†0433004344†04345†0434604347†04349†04350†0435104352†04355†04358†04359†04360†04363†04364†04901†04910†04917†04918†04926†04927†04963†04989†
Penobscot County · 19 mg/L · Soft
04401†04410†04411†0441204417†04418†04419†04422†04427†04428†04430†04434†04435†04444†04448†04449†04450†04453†04455†04456†04457†04460†04461†04468†0446904473†04474†04475†04487†04488†0448904493†04495†04765†04777†04928†04930†04932†04939†04953†04969†
Cumberland County · 17.6 mg/L · Soft
04003†04009†0401104015†04017†04019†0402104024†04029†040320403804039†04040†04050†04055†04057†0406204066†04069†04071†0407404079†04084†0408504091†0409204096†04097†041010410204103041050410604107†0410804109†0411004260†
Somerset County · 15 mg/L · Soft
04478†04911†04912†04920†04923†04924†04925†04929†04937†04942†04943†04944†04945†04950†04957†04958†04961†04965†04967†04971†0497504976†04978†04979†04985†
Piscataquis County · 12.9 mg/L · Soft
04406†04414†0441504426†04441†04442†04443†04462†04463†04464†04479†04481†04485†
Hancock County · 11.6 mg/L · Soft
04408†04416†04421†04429†04431†04472†04476†04605†04607†04609†04612†04613†04614†04616†04617†04624†04625†04627†04634†04635†04640†04642†04646†04650†04653†04660†04662†04664†04669†04673†04674†04675†04676†04677†04679†04681†04683†04684†04685†04693†
Washington County · 11.3 mg/L · Soft
04413†04424†04454†04490†04491†04492†04606†04611†04619†04622†04623†04626†04628†04630†04631†04643†04648†04649†04652†04654†04655†04657†04658†04666†04667†04668†04671†04680†04686†04691†04694†
Oxford County · 6 mg/L · Soft
03579†04010†04022†04037†04041†04051†04068†04088†04216†04217†04219†04220†04221†04224†04226†04227†04231†04237†04238†04255†04257†04261†04267†04268†04270†0427104275†04276†04281†04286†04289†04290†04292†04964†
† 350 ZIP codes are not served by a mapped community water system — most are private-well areas. See well water hardness.
Source
Groundwater vs surface water
Maine's groundwater measures harder than its surface water — 49.1 mg/L across 1,080 samples versus 13 across 2,409, about 3.8× harder. Wells draw from groundwater, so well owners in Maine tend to see the harder number — 49.1 mg/L, soft. Groundwater readings there run 12 to 160 mg/L across the middle 80% of samples. The comparison draws on 725 groundwater and 214 surface-water monitoring sites; 22 readings above 2,000 mg/L were logged but held out of the medians as outliers.
Groundwater (wells)
49.1 mg/L as CaCO₃ · 1,080 results at 725 stations.
Surface water (rivers, lakes)
13 mg/L as CaCO₃ · 2,409 results at 214 stations.
Groundwater measures about 3.8× harder than surface water here.
Chemistry
Water chemistry in Maine
Beyond the hardness number, Maine's water carries a fuller chemical signature — here is how its measured parameters compare to national benchmarks.
TDS
26.5 mg/L · n=192
26.5 mg/L — below the national county median of 226.
pH
6.5 pH · n=485
pH 6.5 — within the EPA secondary range of 6.5–8.5, on the acidic side.
Alkalinity
43 mg/L as CaCO3 · n=600
43 mg/L — modest buffering capacity.
Calcium : Magnesium
2.8 : 0.7 mg/L ≈ 4 : 1 · n=962
Calcium is about 71% of Maine's hardness (2.8 mg/L Ca to 0.7 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 Maine
Two aquifer systems supply much of Maine's measured groundwater.
- New York and New England crystalline-rock aquifers — median 65.5 mg/L across 97 samples at 44 sites: moderately hard.
- Sand and gravel aquifers (glaciated regions) — median 44 mg/L across 350 samples at 185 sites: soft.
Together these systems account for 447 measured samples at 229 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
Maine's decade median moved from 145 mg/L in the 1950s to 4.5 in the 2020s. Over the series, the decade median peaked at 145 mg/L in the 1950s and bottomed at 4.5 in the 2020s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.
Scale
Where Maine sits on the scale
On the USGS scale, Maine's 16.3 mg/L is soft — 1 grains per gallon, below the 60 mg/L soft cutoff — among the softest water measured in the US.
Questions
Frequently asked questions
- Is Maine's water hard?
- Maine's median hardness is 16.3 mg/L as CaCO₃, "soft" on the USGS scale and below the national county median of 140 mg/L.
- Which county in Maine has the hardest water?
- York County, with a median of 53.5 mg/L as CaCO₃ across 105 measurements.
- Is well water harder than city water in Maine?
- Groundwater measures harder here — about 3.8× the surface water — so wells tend to run harder (groundwater 49.1 vs surface water 13 mg/L).
- How do I find my exact hardness in Maine?
- Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
- Is Maine's water harder than the national average?
- No. Maine's median of 16.3 mg/L is below the national county median of 140 mg/L; it ranks #51 of the 50 states and D.C.
Compare
States with similar hardness
Two states measure closest to Maine's 16.3 mg/L: South Carolina at 19 mg/L and Rhode Island at 20.2 mg/L. Maine measures harder than 0% of states. Browse the full ranking on the statistics page.
More: hardness scale · check your address · national statistics · the national map.
By Marko Visic, MPharm, BSc Physics. Source: USGS/EPA Water Quality Portal — 3,490 Maine measurements. Data last verified . Methodology.
Cite this page: “Maine Water Hardness by County.” Hard Water Map. Retrieved 2026-07-22, https://hardwatermap.com/water-hardness/maine/