The East Maui Irrigation System is Hawaii's most dramatic water story. It began with the construction of the Old Hamakua Ditch built between 1876 and 1878. This privately financed, constructed and managed irrigation system was one of the largest in the United States. It eventually included 50 miles of tunnels; 24 miles of open ditches, inverted siphons and flumes; incorporates approximately 400 intakes and 8 reservoirs. The aqueducts bring water from steep tropical forest dissected by many ravines on the Windward and wet slopes of Haleakala, a 10,000 foot high dormant volcano, to the fertile semi-arid central Maui isthmus. They provide half the irrigation water to the sugar growing area of Maui.
This irrigation system demonstrated the feasibility of transporting water from steep tropical forested watersheds with high rainfall across difficult terrain to fertile and dry plains. Over the years of the development of this system, many engineers gained experience in building irrigation systems. They used what they learned from the East Maui Irrigation System to develop irrigation systems for the Western United States. For instance, engineer M.M. O'Shaughnessey, in charge of constructing the Koolau Ditch in 1904 and 1905, subsequently built the San Francisco Hetch Hetchy water system.