Waipahu, HI water hardness

Tap water hardness
55mg/L
3.2gpg
SoftCounty estimate

County estimate from 114 water samples in Honolulu County · July 2026

HI typical
55 mg/L
Data
County estimate

Water samples from around Waipahu put hardness at about 55 mg/L (3.2 gpg), which would be soft on the USGS scale. Treat this as a rough guide: it is the median of 114 samples taken across Honolulu County, mostly wells and streams, not a test of Waipahu's treated tap water.

Waipahu on the hardness scale, with nearby cities
060120180240300360+HI typical 55Honolulu: 55 mg/LHonolulu 55Pearl City: 102 mg/LPearl City 102Iroquois Point: 102 mg/LIroquois Point 102Ewa Beach: 102 mg/LEwa Beach 102Waimalu: 102 mg/LWaimalu 102Hickam Housing: 102 mg/LHickam Housing 102Aiea: 102 mg/LAiea 102Halawa: 102 mg/LHalawa 102Ahuimanu: 105 mg/LAhuimanu 105Kahaluu: 105 mg/LKahaluu 105Waipahu 55mg/L as calcium carbonate060120180240300360+HI 55Pearl City: 102 mg/LPearl City 102Iroquois Point: 102 mg/LIroquois P. 102Ewa Beach: 102 mg/LEwa Beach 102Waimalu: 102 mg/LWaimalu 102Hickam Housing: 102 mg/LHickam Hou. 102Aiea: 102 mg/LAiea 10255 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

At 55 mg/L, Waipahu is close to the typical Hawaii figure of 55 mg/L. None of the 10 nearest cities we track has softer water. The range nearby runs from 55 mg/L in Honolulu to 105 in Ahuimanu.

What 55 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 55 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 Waipahu's water system

We could not match Waipahu 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 Waipahu water hard?

No. It measures about 55 mg/L (3.2 grains per gallon), which the USGS classes as soft.

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

About 3.2 gpg. One grain per gallon equals 17.1 mg/L, so 55 mg/L divided by 17.1 gives 3.2.

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.