Waipahu Water Hardness & Quality Report (2026)

Waipahu, Hawaii, a community in Honolulu County on the central Ewa Plain of Oahu — a historically significant plantation community (Waipahu was the site of the Oahu Sugar Company — one of Hawaii's major sugar plantations, established in 1897, closing in 1995 — Waipahu Sugar Mill was the central plantation mill for central Oahu), a diverse central Oahu community with significant Filipino-American, Micronesian-American, and Pacific Islander communities (Waipahu has one of the highest concentrations of Filipino-Americans in Hawaii), adjacent to Pearl City and Ewa Beach, and a working-class and middle-class central Oahu suburban community — draws its municipal water supply from the Pearl Harbor Basal Lens Aquifer via the Honolulu Board of Water Supply (BWS). Water hardness in Waipahu measures 28 mg/L — classified as very soft.

Waipahu's exceptional softness reflects the central Oahu Ko'olau basaltic volcanic aquifer's calcareous-poor geology. The Pearl Harbor Basal Lens Aquifer at Waipahu–central Oahu draws from: the Ko'olau Basalt (calcareous-poor tholeiitic basalt — minimal carbonate content); the Wai'anae Volcanics (calcareous-poor older basalt). The heavy Ko'olau orographic rainfall infiltrates through the calcareous-poor basalt, producing very soft water. BWS central Oahu distribution produces the exceptional 28 mg/L at Waipahu.

With hardness at 28 mg/L, Waipahu residents enjoy exceptionally soft water. BWS consistently delivers water meeting all Hawaii DOH and EPA Safe Drinking Water Act requirements.