How hard is the water in Kalawao County, HI?

2.1 grains per gallon

You do not need a softener here.

The median hardness measured in Kalawao County, HI is 37 mg/L as calcium carbonate, which is 2.1 gpg. That is soft on the USGS scale. It comes from 40 samples at 1 sites between 1994 and 1995, drawn from every sampling site in the county, wells and surface water together.

How much it varies here

Half the sites came in between 2.1 and 2.1 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: low (how it is measured).

What to do next

You can skip the softener. At 2.1 gpg the most a softener would fix is the odd water spot. If a salesperson in Kalawao County says otherwise, ask to see their reading in grains per gallon and compare it with this one.

More on when a softener is not worth it.

From 2.1 to 2.1 gpg

The softest single sample on record in Kalawao County was 36.5 mg/L and the hardest 36.5 mg/L, a 1-fold gap. The top quarter of sites read above 2.1 gpg and the bottom quarter below 2.1 gpg.

Kalawao County against the rest of Hawaii

Among the 5 Hawaii counties with data, Kalawao County is the softest. Across the whole country it is harder than 17% of counties.

Hardest: Maui County at 24.7 gpg. Closest to Kalawao County: Kauai County (2.6), Honolulu County (3.6), Hawaii County (4).