In ancient times, Oahu's earliest inhabitants, the native Hawaiians, drew their water supplies from fresh water springs, lakes, streams and shallow wells. Ancient Hawaiians survived through wise management of land and water. The use of strict kapu/laws were passed called the kanawai and basically, damaging or harming water sources were serious crimes that were severely punishable. 

Ancient Hawaiians understood the importance of their limited supply of water because they were surrounded by salt water. In the 1700’s ancient Hawaiians had an advanced irrigation system that enabled them to turn vast areas into farm lands before the westerners arrived. They developed sophisticated sustainable water management strategies that kept water flowing and went from mountain to sea
managed land in ahupua’a- now a modern and successful idea called a watershed. A watershed is a diverse and highly organized ecosystem which specializes in the capturing of rain and atmospheric moisture from the air and sky.
located in high mountains or valleys, which then divert the water into rivers and streams. Watersheds are composed of several layers of dense vegetation.  Oahu's watershed can also be described as a Hawaiian rain forest, which captures and saves large amounts of water.