How hard is the water in Maui County, HI?
24.7 grains per gallon
A softener will pay its way here.
The median hardness measured in Maui County, HI is 424 mg/L as calcium carbonate, which is 24.7 gpg. That is very hard on the USGS scale. It comes from 10 samples at 10 sites between 1990 and 2023, drawn from groundwater wells, which is what most taps and private wells in the county draw on.
How much it varies here
Half the sites came in between 13 and 31.8 gpg. The whole middle of that range gives the same answer, so a test of your own tap is unlikely to change it. Confidence in the county figure: medium (how it is measured).
What to do next
At 24.7 gpg a softener pays its way here. Before you buy, check the quoted unit's grain capacity against the sizing table below, and ask whether it regenerates on demand, which uses less salt than a timer. Call your utility for its own report if you are on city water.
More on sizing a softener for your household.
From 2.8 to 255.9 gpg
The softest single sample on record in Maui County was 48.1 mg/L and the hardest 4,380 mg/L, a 91-fold gap. The top quarter of sites read above 31.8 gpg and the bottom quarter below 13 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 24.7 gpg, rivers and lakes 0.8 gpg
10 groundwater samples from 10 wells put the median at 423.5 mg/L. 342 surface samples from 11 sites put it at 13.5 mg/L. In Maui County the wells come out 23.9 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. A utility here that draws from the river can deliver noticeably different water from a private well next door.
What a softener would cost to run
For a household of 3, a 32,000-grain unit covers a week between regenerations. Expect about 540 lb of salt a year (14 bags of 40 lb, about $97), and roughly 2,346 gallons of regeneration water. Installed, most units run $1,000 to $4,500; spread over 15 years with salt, that is about $197 a year.
Sizing at 24.7 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,482 | 24,000 | 180 lb |
| 2 | 2,964 | 24,000 | 361 lb |
| 4 | 5,928 | 48,000 | 721 lb |
| 6 | 8,892 | 64,000 | 1,082 lb |
Maui County against the rest of Hawaii
Among the 5 Hawaii counties with data, Maui County is the hardest. Across the whole country it is harder than 91% of counties.
Softest in Hawaii: Kalawao County at 2.1 gpg. Closest to Maui County: Hawaii County (4), Honolulu County (3.6), Kauai County (2.6).