Hawai'i Kai Water Hardness & Quality Report (2026)
Water Hardness
3.3 grains per gallon
Source
groundwater
pH Level
7.5
neutral = 7.0
Lead
0.006 mg/L
✓ Below action level
TDS
166.8 mg/L
Est. Daily Cost
$0.15
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 Hawai'i Kai, your appliances are currently losing 7% efficiency due to mineral buildup.
| Appliance | In Hawai'i Kai | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 7.8 yrs | 8.5 yrs | -8% |
| Washing Machine | 11.5 yrs | 12 yrs | -4% |
| Water Heater | 13.4 yrs | 15 yrs | -11% |
Regional Water Comparison
How Hawai'i Kai compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Hawai'i Kai, Hawaii | 56 mg/L | 1.2 ppt | 🟢 Soft | groundwater |
| East Honolulu, Hawaii | 31 mg/L | 0.8 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 Hawai'i Kai compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Hawai'i Kai | 56 mg/L | 🟢 None |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Hawai'i Kai's Water Unique?
Local geology and source profile
Hawaii Kai, Honolulu, Hawaii — a major east Honolulu residential and marina community (Hawaii Kai is one of the most distinctive and desirable residential communities on Oahu — a planned residential community in the scenic east Honolulu Maunalua Bay area, built largely on land developed by Henry J. Kaiser (the famous industrialist) beginning in the 1960s; Hawaii Kai's marina system (one of the most significant small boat marina communities in Hawaii) and the surrounding volcanic ridges, beaches, and Koko Head Crater make it one of the most scenic communities on Oahu), home of Hanauma Bay Nature Preserve (one of the most visited snorkeling destinations in Hawaii — the protected marine sanctuary in the ancient volcanic crater bay at the eastern end of Honolulu), home of the Koko Head Crater (a volcanic tuff cone with stunning views of the windward Oahu coastline), a diverse Honolulu County community with a significant Japanese-American, Chinese-American, Korean-American, and affluent professional population (Hawaii Kai is one of the more expensive residential areas in Honolulu) — draws its municipal water supply via the Honolulu BWS. Water hardness in Hawaii Kai measures 56 mg/L — classified as moderately soft.
Hawaii Kai's moderate softness reflects the east Oahu Koolau Basalt aquifer's calcareous-poor volcanic character with some distribution variation. The Koolau Range basalt aquifer provides water from the Quaternary Koolau Shield Volcano Basalt (calcareous-poor). Honolulu BWS produces the moderately soft 56 mg/L for the east Oahu zone.
With hardness at 56 mg/L, Hawaii Kai residents enjoy moderately soft water. Honolulu BWS consistently delivers water meeting all Hawaii DOH and EPA Safe Drinking Water Act requirements.
Geology & Source: Groundwater from the Koolau Range basal lens aquifer via the Honolulu Board of Water Supply (BWS) — the Honolulu County east Oahu Hawaii Kai corridor (Quaternary calcareous-poor Koolau Basalt — the extremely calcareous-poor east Oahu shield volcano basalt aquifer; Honolulu BWS east Oahu distribution); moderately soft supply at 56 mg/L in Honolulu County.