Wailuku Water Hardness & Quality Report (2026)

Wailuku, Hawaii, in Maui County — the Maui County seat adjacent to Kahului and Waikapu on central Maui in the Iao Valley — receives its water from the Maui Department of Water Supply, drawing from the Iao Aquifer (West Maui Mountains, Maui County) through the central Maui distribution.

The very soft 23 mg/L hardness and very low TDS of 55.1 mg/L reflect the central Maui Iao Aquifer's nearly insoluble volcanic basalt character — among the softest municipal supplies in the USA. The Iao Aquifer at Wailuku is developed in Pleistocene Wailuku Basalt (basalt — insoluble — primary aquifer rock), Pleistocene West Maui Volcanics (basalt — insoluble), and young Holocene alluvial deposit (minimal mineral loading). The entirely insoluble volcanic basalt geology of the West Maui Mountains produces the very soft central Maui supply.

At 23 mg/L, Wailuku's water is very soft — essentially no scale forms, soap lathers abundantly, and appliances maintain excellent efficiency. Annual descaling is sufficient. The PFAS level of 0.7 ppt is essentially zero — the Maui County central Maui corridor has virtually no industrial PFAS sources, and the pristine Hawaiian volcanic aquifer system produces some of the cleanest water in the entire USA dataset.