Over the years, O’ahu’s water resources have played a crucial role in shaping the island’s development and sustainability. Hawaiians tapped into natural springs and streams during ancient times to create an intricate network of irrigation systems that supported agriculture on the island. O’ahu became a regular stop for whalers seeking to refill their ships’ barrels with fresh water for drinking.

Before Hawaii became a territory of the US in 1900, the Minister of the Interior of Hawaii was responsible for maintaining O’ahu water quality through Honolulu’s Water Works. In 1913, the Department of Public Works took over O’ahu tap water distribution. The island faced many water shortage issues until The Board of Water Supply was created in 1929. The BWS established an effective water management system that helped improve O’ahu drinking water quality and availability. 

The Board of Water Supply is still in charge of monitoring and maintaining O’ahu water quality and O’ahu tap water is generally safe to drink. The majority of O’ahu residents—about 98%—get tap water delivered to their homes via an interconnected system of underground shafts, water tunnels, and wells. Water is pumped through this system from onshore aquifers that provide all of O’ahu’s fresh water. Water travels through layers of soil and volcanic rock in these aquifers and is purified through percolation.

Water shortages have been an issue for O’ahu over the years and the island is still recovering from over-pumping groundwater sources in the 1900s. The Hawaii State Legislature passed the State Water Code to better monitor O’ahu tap water distribution and the Hawaii State Department of Health is now responsible for protecting groundwater resources. Only time will tell if these changes will have an impact on the damage done to O’ahu’s fresh water supply.

O’ahu water quality is affected by agricultural chemicals, septic waste, mining, and other factors that can contaminate groundwater sources. Though O’ahu water quality meets all federal and state requirements, both arsenic and lead have been found in O’ahu tap water.