Though Hawaii is surrounded by the expansive Pacific Ocean, life on the islands requires not only salt water but fresh water supplied to the land by falling rain. Rainfall totals vary wildly depending on location.
Between 25 and 30 inches of rain fall per year on the ocean near Hawaii, according to the National Oceanic and Atmospheric Administration. But the islands receive as little as one-third of that in some places and as much as 15 times that much elsewhere because moisture brought by trade winds condenses and falls when clouds hit mountains and rise. Mount Waialeale in the center of Kauai is among the wettest places on earth with average annual rainfall of more than 400 inches.
After rain falls, some of it is channeled into mountain streams that eventually feed rivers that meet the sea. The rest is absorbed into the ground, with some of it finding its way to aquifers where it is stored as ground water, accessible only through pumping wells. As the water flows down from the mountains, it is used by animals and plants for their survival.
Because some areas are generally more arid due to rain shadows or other natural phenomenon, humans have devised systems to distribute water far and wide. Many of the technological breakthroughs, such as complex diversion systems, were made to make farming financially successful for export crops like pineapple and sugar. Use of the ditch systems is managed today by the Commission on Water Resource Management.
For centuries after their arrival from Polynesia, Native Hawaiians divided the land into ahupuaa — subdivisions running from the ocean to the mountains, roughly defined by their watersheds. Fresh water flowed through taro patches, where it supported the Hawaiians' staple crop. It eventually reached the sea, where it enriched fishponds and reefs, which in turn support life in the ocean.
Even after Western contact, the definition of water as a public resource was included in some of the first written laws in Hawaii. From the first constitution of the Kingdom of Hawaii in 1840 to Chapter 11 of the Hawaii State Constitution to the Water Code — Chapter 174C of the Hawaii Revised Statutes — in the late 1980s, water has been held for the citizens. This idea is in stark contrast to the concept of water as a private property right.
The Water Code established the State of Hawaii Commission on Water Resource Management, which falls under the Hawaii Department of Land and Natural Resources and is tasked with the protection and enhancement of the state's water resources through "wise and responsible management." It accomplishes this by administering the Hawaii Water Plan and Hawaii Administrative Rules and regulating the use of water by, among other things, determining how much water can be diverted from streams for private uses.