Rhode Island Water Hardness by County
Water in Rhode Island has a median hardness of 20.2 mg/L as CaCO₃ — "soft" on the USGS scale — based on 3,496 measurements at 538 monitoring stations. Providence County has the state's hardest measured water (23.9 mg/L); Kent County the softest (12.9). Rank: #49 of the 50 states and D.C.
Rhode Island water hardness map — what the numbers mean. Data verified 2026-07-22.
Of Rhode Island's 4 measured counties, 4 soft. The hardest are Providence County (23.9 mg/L), Newport County (18.4), and Washington County (17). Kent County is the softest at 12.9 mg/L (soft).
No measured Rhode Island 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, Rhode Island's median works out to 1.2 grains per gallon and ranks #49 of the 50 states and D.C. Across 3,496 measurements at 538 stations — 2,671 of them since 2000 — the middle 80% of readings fall between 9.5 and 57.1 mg/L. The public record runs from 1925 to 2023.
See where Rhode Island sits nationally on the national map, or what its number means on the hardness scale.
Download the Rhode Island water hardness map (PNG) — Water hardness by county in Rhode Island: 4 counties mapped from USGS/EPA data, statewide median 20.2 mg/L (soft); darker counties have harder water.
By county
Water hardness by county
The table lists all 4 measured Rhode Island counties, hardest first. Their medians span 23.9 mg/L in Providence County to 12.9 in Kent County — a 1.9× range. 1 more Rhode Island county lacks gate-passing data.
| County | Median | Band | Results | Sites | Newest |
|---|---|---|---|---|---|
| Providence County | 23.9 | Soft | 1,838 | 126 | 2023 |
| Newport County | 18.4 | Soft | 8 | 4 | 2016 |
| Washington County | 17 | Soft | 562 | 112 | 2023 |
| Kent County | 12.9 | Soft | 58 | 30 | 1999 |
| 1,024 additional results from sites without county attribution (not shown). | |||||
ZIP codes
ZIP codes in Rhode Island
The ZIP codes below are grouped by the Rhode Island 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.
Providence County · 23.9 mg/L · Soft
0280202814†02815†02823†0282402825†02826†0282802829†02830†02831†0283802839†02857†02858†02859†0286002861028630286402865028760289502896†0290302904029050290602907029080290902910029110291202914029150291602917†0291802919†0292002921
Newport County · 18.4 mg/L · Soft
0283502837†02840†02841†028420287102872†02878†
Washington County · 17 mg/L · Soft
02804†02807†0280802812†02813†02822†02832†02833†02836†0285202873†02874†02875†02879028810288202891†02892†02894†02898†
Kent County · 12.9 mg/L · Soft
02816†02817†0281802827†02886†028880288902893
† 39 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
Rhode Island's groundwater measures harder than its surface water — 31.2 mg/L across 168 samples versus 18.9 across 2,485, about 1.7× harder. Wells draw from groundwater, so well owners in Rhode Island tend to see the harder number — 31.2 mg/L, soft. Groundwater readings there run 10.8 to 82.6 mg/L across the middle 80% of samples. The comparison draws on 126 groundwater and 184 surface-water monitoring sites; 20 readings above 2,000 mg/L were logged but held out of the medians as outliers.
Groundwater (wells)
31.2 mg/L as CaCO₃ · 168 results at 126 stations.
Surface water (rivers, lakes)
18.9 mg/L as CaCO₃ · 2,485 results at 184 stations.
Groundwater measures about 1.7× harder than surface water here.
Chemistry
Water chemistry in Rhode Island
Beyond the hardness number, Rhode Island's water carries a fuller chemical signature — here is how its measured parameters compare to national benchmarks.
TDS
86.5 mg/L · n=20
86.5 mg/L — below the national county median of 226.
pH
6.8 pH · n=2,096
pH 6.8 — within the EPA secondary range of 6.5–8.5, on the acidic side.
Alkalinity
15.6 mg/L as CaCO3 · n=142
15.6 mg/L — modest buffering capacity.
Calcium : Magnesium
6.2 : 1.4 mg/L ≈ 4.43 : 1 · n=1,697
Calcium is about 73% of Rhode Island's hardness (6.2 mg/L Ca to 1.4 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 Rhode Island
One aquifer system supply much of Rhode Island's measured groundwater.
- Sand and gravel aquifers (glaciated regions) — median 43.3 mg/L across 47 samples at 34 sites: soft.
Together these systems account for 47 measured samples at 34 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
Rhode Island's decade median moved from 23 mg/L in the 1950s to 18.3 in the 2020s. Over the series, the decade median peaked at 23 mg/L in the 1950s and bottomed at 18.3 in the 2020s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.
Scale
Where Rhode Island sits on the scale
On the USGS scale, Rhode Island's 20.2 mg/L is soft — 1.2 grains per gallon, below the 60 mg/L soft cutoff — among the softest water measured in the US.
Questions
Frequently asked questions
- Is Rhode Island's water hard?
- Rhode Island's median hardness is 20.2 mg/L as CaCO₃, "soft" on the USGS scale and below the national county median of 140 mg/L.
- Which county in Rhode Island has the hardest water?
- Providence County, with a median of 23.9 mg/L as CaCO₃ across 1,838 measurements.
- Is well water harder than city water in Rhode Island?
- Groundwater measures harder here — about 1.7× the surface water — so wells tend to run harder (groundwater 31.2 vs surface water 18.9 mg/L).
- How do I find my exact hardness in Rhode Island?
- Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
- Is Rhode Island's water harder than the national average?
- No. Rhode Island's median of 20.2 mg/L is below the national county median of 140 mg/L; it ranks #49 of the 50 states and D.C.
Compare
States with similar hardness
Two states measure closest to Rhode Island's 20.2 mg/L: Mississippi at 21.1 mg/L and South Carolina at 19 mg/L. Rhode Island measures harder than 4% 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 — 3,496 Rhode Island measurements. Data last verified . Methodology.
Cite this page: “Rhode Island Water Hardness by County.” Hard Water Map. Retrieved 2026-07-22, https://hardwatermap.com/water-hardness/rhode-island/