Kahului, HI water hardness

Tap water hardness
20mg/L
1.2gpg
SoftCounty estimate

County estimate from 108 water samples in Maui County · July 2026

HI typical
55 mg/L
Data
County estimate

Water samples from around Kahului put hardness at about 20 mg/L (1.2 gpg), which would be soft on the USGS scale. Treat this as a rough guide: it is the median of 108 samples taken across Maui County, mostly wells and streams, not a test of Kahului's treated tap water.

Kahului on the hardness scale, with nearby cities
060120180240300360+HI typical 55Pukalani: 12 mg/LPukalani 12Kula: 12 mg/LKula 12Lahaina: 32 mg/LLahaina 32Kihei: 51 mg/LKihei 51Honolulu: 55 mg/LHonolulu 55Kailua: 103 mg/LKailua 103East Honolulu: 105 mg/LEast Honolulu 105Waimanalo: 105 mg/LWaimanalo 105Kaneohe: 105 mg/LKaneohe 105Wailuku: 150 mg/LWailuku 150Kahului 20mg/L as calcium carbonate060120180240300360+HI 55Pukalani: 12 mg/LPukalani 12Kula: 12 mg/LKula 12Lahaina: 32 mg/LLahaina 32Kihei: 51 mg/LKihei 51East Honolulu: 105 mg/LEast Honol. 105Wailuku: 150 mg/LWailuku 15020 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

Kahului sits 35 mg/L below the typical Hawaii figure of 55. Of the 10 nearest cities we track, 2 have softer water and 8 have harder. The range nearby runs from 12 mg/L in Pukalani to 150 in Wailuku.

What 20 mg/L means at home

Soap and shampoo lather with very little product. Kettles and showerheads stay mostly free of white crust.

Some people notice that soap feels slow to rinse off in soft water. That slippery feel is normal and harmless.

Hardness is not a health problem, and EPA sets no limit for it. It is a matter of scale and soap.

What to do about it

Nothing, as far as hardness goes. At 20 mg/L a softener would have almost nothing to remove.

Carbon filter

If the water tastes of chlorine, a pitcher or faucet carbon filter takes care of that. It does not change hardness.

EPA record for Kahului's water system

We could not match Kahului to a community water system in EPA's records. Your water bill or the yearly Consumer Confidence Report names the system and its ID.

Questions

Is Kahului water hard?

No. It measures about 20 mg/L (1.2 grains per gallon), which the USGS classes as soft.

What is the water hardness in Kahului in grains per gallon?

About 1.2 gpg. One grain per gallon equals 17.1 mg/L, so 20 mg/L divided by 17.1 gives 1.2.

Nearby cities

All 23 cities in Hawaii

Hardness data: TapWaterData US Water Hardness (county estimate, July 4, 2026), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.