Makakilo Water Hardness & Quality Report (2026)

Makakilo, Hawaii, receives drinking water from the Honolulu Board of Water Supply (BWS), specifically through the Ewa-Waianae water system. The primary source is the Makakilo Well, tapping into the Waianae Aquifer system on Oahu's leeward coast. No specific treatment plants are identified for this well, but BWS applies standard groundwater treatment including chlorination for disinfection, with active monitoring for emerging contaminants. The service area covers Makakilo in Honolulu County, serving residential and community needs in this Kapolei-adjacent neighborhood on Oahu's western leeward coast.

The Waianae Groundwater Basin on Oahu's leeward side is hosted within the Waianae Mountains, composed of Miocene Waianae Volcanic Series rocks — predominantly tholeiitic basalt flows, pyroclastics, and minor intrusions approximately 15–20 million years old. Rainwater infiltrates these fractured, porous formations, forming a freshwater lens floating atop denser seawater. Basalt weathers to yield minimal dissolved calcium and magnesium, resulting in characteristically soft water with low dissolved solids — typical of Pacific island basal groundwater systems.

With soft water, Makakilo residents experience minimal scale buildup in pipes, water heaters, dishwashers, and washing machines, and appliances last longer due to the absence of mineral deposits. Soap and detergents lather efficiently; no water softener is needed or recommended. Periodic filter cleaning for any sediment from volcanic sourcing is advisable. Recent testing detected low PFPeA levels (0.0021–0.0023 µg/L) at the Makakilo Well — far below Hawaii DOH's 0.8 µg/L EAL — with BWS confirming full compliance with Hawaii and federal standards; pH, lead, and copper data align with federal rules per 2023 CCRs.