Royal Kunia Water Hardness & Quality Report (2026)

Royal Kunia, Hawaii, in Honolulu County — an unincorporated Honolulu County community adjacent to Waipahu and Ewa Beach in the central Oahu Ewa Plain — receives its water from the Honolulu Board of Water Supply (BWS), drawing from the Oahu Basal Aquifer (Honolulu County) through the central Oahu distribution.

The moderately soft 76.5 mg/L hardness and TDS of 255.5 mg/L (TDS elevated relative to hardness — reflecting the basal lens aquifer's slight saline ocean margin mixing at the Ewa Plain coastal position) reflect the central Oahu Basal Aquifer's predominantly insoluble volcanic basalt character. The Oahu Basal Aquifer at Honolulu County is developed in Pleistocene-Holocene Koolau Basalt (volcanic — near-insoluble, primary supply) and Pleistocene Waianae Basalt (volcanic — near-insoluble), with the basal freshwater lens sitting above saline ocean water (causing slightly elevated TDS at the coastal Ewa Plain position near Royal Kunia).

At 76.5 mg/L, Royal Kunia's water is soft — light scale forms slowly in appliances, dishwashers remain efficient, and bathroom fixtures need occasional cleaning. Semi-annual descaling is appropriate. The PFAS level of 1.5 ppt is very low — the Oahu central Hawaii military corridor (Schofield Barracks and Wheeler Army Airfield — AFFF, adjacent to central Oahu) contributes minor readings, remaining among the lowest PFAS levels in the USA dataset.