East Honolulu Water Hardness & Quality Report (2026)
Water Hardness
1.8 grains per gallon
Source
groundwater
pH Level
7.3
neutral = 7.0
Lead
0.003 mg/L
✓ Below action level
TDS
78.6 mg/L
Est. Daily Cost
$0.08
energy & soap waste
Source: USGS Water Quality Portal · Updated 2026
0–60
mg/L
Soft
61–120
mg/L
Moderately Hard
121–180
mg/L
Hard
180+
mg/L
Very Hard
Appliance Damage Report
In East Honolulu, your appliances are currently losing 4% efficiency due to mineral buildup.
| Appliance | In East Honolulu | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 8.6 yrs | 8.5 yrs | — |
| Washing Machine | 12.5 yrs | 12 yrs | — |
| Water Heater | 14.4 yrs | 15 yrs | -4% |
Regional Water Comparison
How East Honolulu compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ East Honolulu, Hawaii | 31 mg/L | 0.8 ppt | 🟢 Soft | groundwater |
| Hawai'i Kai, Hawaii | 56 mg/L | 1.2 ppt | 🟢 Soft | groundwater |
| Niu Valley, Hawaii | 79.5 mg/L | 1.5 ppt | 🟡 Moderately Hard | groundwater |
| Kuliouou - Kalani Iki, Hawaii | 57.5 mg/L | 1.2 ppt | 🟢 Soft | groundwater |
| Palolo, Hawaii | 27 mg/L | 0.8 ppt | 🟢 Soft | groundwater |
National Benchmark
How East Honolulu compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ East Honolulu | 31 mg/L | 🟢 None |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes East Honolulu's Water Unique?
Local geology and source profile
East Honolulu, Hawaii, in Honolulu County on the southeast coast of Oahu — an upscale Honolulu community encompassing Hawaii Kai, Aina Haina, Portlock, Kuliouou, and the Koolau Range coastal neighborhoods, known for Hawaii Kai Marina, Hanauma Bay Nature Preserve, and some of Honolulu's most affluent residential areas — draws its municipal water supply from the Oahu basal freshwater lens and dike-impounded groundwater via the Honolulu Board of Water Supply (BWS). Water hardness in East Honolulu measures 31 mg/L — classified as extremely soft.
East Honolulu's extremely soft supply reflects Oahu's calcium-poor volcanic geology. The Koolau Basalt (Pliocene–Quaternary Koolau Volcanic Series — the dominant basalt of the Koolau Mountain Range) is a tholeiitic to alkalic basalt of oceanic island origin, containing minimal calcareous minerals (basalt is calcium-moderate in the plagioclase fraction but dissolves minimally under Hawaii's tropical freshwater recharge conditions). The basal freshwater lens in the Koolau basalt — recharged by direct rainfall on the Koolau Mountains (among the highest rainfall areas in the world) — has very short groundwater residence time in young basalt, producing extremely soft rainwater-dominated groundwater of 31 mg/L at East Honolulu.
With hardness at 31 mg/L, East Honolulu residents enjoy some of the softest water in the United States. Honolulu Board of Water Supply consistently delivers water meeting all Hawaii DOH and EPA Safe Drinking Water Act requirements.
Geology & Source: Groundwater from the Honolulu Board of Water Supply (BWS) basal freshwater lens and dike-impounded aquifer via the Honolulu BWS — the Honolulu District southeast Oahu (Quaternary–Pliocene Koolau Basalt basal lens aquifer at the Waialae–Hawaii Kai corridor); extremely soft supply at 31 mg/L — reflecting Oahu's calcium-poor Koolau Basalt volcanic terrain.