Kapolei Water Hardness & Quality Report (2026)
Water Hardness
2.9 grains per gallon
Source
groundwater
pH Level
7.4
neutral = 7.0
Lead
0.005 mg/L
✓ Below action level
TDS
139.7 mg/L
Est. Daily Cost
$0.13
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 Kapolei, your appliances are currently losing 7% efficiency due to mineral buildup.
| Appliance | In Kapolei | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 8 yrs | 8.5 yrs | -6% |
| Washing Machine | 11.8 yrs | 12 yrs | -2% |
| Water Heater | 13.6 yrs | 15 yrs | -9% |
Regional Water Comparison
How Kapolei compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Kapolei, Hawaii | 49 mg/L | 1.1 ppt | 🟢 Soft | groundwater |
| 'Ewa Gentry, Hawaii | 38 mg/L | 0.9 ppt | 🟢 Soft | groundwater |
| Makakilo City, Hawaii | 55 mg/L | 1.2 ppt | 🟢 Soft | groundwater |
| Makakilo, Hawaii | 75.5 mg/L | 1.5 ppt | 🟡 Moderately Hard | groundwater |
| Makakilo / Kapolei / Honokai Hale, Hawaii | 35.5 mg/L | 0.9 ppt | 🟢 Soft | groundwater |
National Benchmark
How Kapolei compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Kapolei | 49 mg/L | 🟢 None |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Kapolei's Water Unique?
Local geology and source profile
Kapolei, Hawaii, in Honolulu County — an unincorporated Honolulu County community adjacent to Ewa Beach and Makakilo City on the southwest Oahu coastal plain — receives its water from the Honolulu Board of Water Supply (BWS), drawing from the Pearl Harbor Aquifer (southwest Oahu) through the southwest Oahu distribution.
The soft 49 mg/L hardness and TDS of 139.7 mg/L (elevated TDS relative to hardness — suggesting minor Pacific marine aerosol and coastal infiltration chloride) are consistent with the nearby Makakilo City (55 mg/L) — reflecting the same southwest Oahu Waianae volcanic basalt aquifer character. The Pearl Harbor Aquifer at Kapolei is developed in Pleistocene Waianae Volcanics (basalt — slightly weathered, insoluble primary aquifer), Pleistocene Koolau Basalt (basalt — insoluble), and coastal alluvial caprock (slightly calcareous, marine salt infiltration contribution).
At 49 mg/L, Kapolei's water is soft — light scale forms very slowly in appliances, dishwashers are highly efficient, and bathroom fixtures need minimal cleaning. Annual descaling is sufficient. The PFAS level of 1.1 ppt is very low — the Honolulu County southwest Oahu corridor has minimal PFAS, and the Pearl Harbor Naval Station PFAS (AFFF — historic foam use) is primarily contained to the Pearl Harbor basin and does not significantly reach the Kapolei service zone.
Geology & Source: Kapolei in Honolulu County draws from the Honolulu Board of Water Supply on the Pearl Harbor Aquifer (Honolulu County, southwest Oahu) — the Pearl Harbor Aquifer at Kapolei is developed in Pleistocene Waianae Volcanics basalt (insoluble) — Hawaii Honolulu County Pearl Harbor Waianae volcanic basalt aquifer produces soft water at 49 mg/L with TDS 139.7 mg/L in this Oahu Hawaii city.