Oahu steep mountains are key to the island's ability to attract clouds and abundant rainfall. On young, high mountains such as the Big Island's, clouds drop their precipitation before they are pushed to the highest elevations, leaving the upper reaches dry and desert-like. On older, eroded islands such as Oahu and Kauai, rainfall is heaviest on he windward sloped and mountain peaks, allowing lush vegetation to cover even the highest ridges. A relatively flat island such as Niihau has very little rainfall because it lacks the high elevation slopes. Without the slopes, winds cannot push moist air upwards to produce clouds and precipitation. Rainfall is only one part of the water cycle equation. Oahu also interacts with the skies to funnel water from the atmosphere back to land. The island's topography, augmented by a healthy, balanced natural ecosystem, catches, collects and stores water. A watershed is an area of land, such as mountain or a valley, hat catches and collects rainwater. Topography influences whether rainwater moves toward the sea via rivers and streams or via movement underground. Oahu has two main watersheds, one in the Koolau Mountains and another on the crest of the Waianae Range. The Koolaus run perpendicular to the Northeast trades and experience the heaviest rainfall. The Waianae peaks, though higher, sit in the Koolau rain shadow and receive less rain, even on their windward slopes.
A rainforest is a forest ecosystem in which rainfall is abundant throughout the year. The covering in the forest catches rain and dew and stabilises the upper soil layers, letting rainwater filter through to deeper layers. Forest growth also stabilises stream banks, limiting erosion debris in surface flow. The heavily forested regions on he mountain tops of each island are Hawaii's primary watershed areas. Hawaii native forests have evolved over millions of years to become highly effective watershed covers. Vegetation in the forest fills every level. It soaks up rainfall like a giant sponge, allowing water to drip slowly underground and into streams. When a forest is degraded, rain falling on bare earth causes erosion. The water-retaining upper soil layers are washed away, leaving behind less permeable clays. Water runs off this impermeable surface rather than filtering down to replenish the aquifer. Streams that emanate from deforested mountains flood during rains. When the rains stop, these streams run dry. The loss of stabilising tree and plant roots results in landslides. Debris carried by streams ends up in ocean coastal areas, causing siltation of reefs. When a native forest is eroded and damaged, opportunistic foreign species invade. While these new plants can stabilise bare ground, the watershed cover they create is not as effective as that of the native forest.
In 1879, James Campbell and John Ashley discovered Oahu vas underground water lens. Campbell had purchased 41,000 barren acres on the Ewa plains. He dug 273 feet into the soil and found a gusher of fresh, clean water. Before too long, wells were being bored all over Oahu and suddenly the island's growth seemed limitless. As Oahu rapid growth continued, demands for water escalated. Honolulu's population was swelling and tripled between 1879 and 1915. Outside the city, more and more land was being put into sugar can and other crops, including rice. Everyone it seemed needed more water. In Honolulu, there were some early attempts to oversee water use and development. Outside the city, government oversight was all but nonexistent. Through the end of 1920s, water development on Oahu was widespread and largely unchecked. People took what they needed and left the planning to someone else. The water free-for-all couldn't last forever. With so much water being taken out, the rains could not replenish the aquifer. Wells began to salt up or dry up altogether.
In 1929, after a series of events, the Legislature took unilateral control of water from the City and turned it over to a newly created semi-autonomous city agency, the Honolulu Board of Water Supply. The newly created board was given broad powers over water to develop it, sell it and plan for its future on Oahu. It used the mandate to create the island's first truly effective water management system. All of the effort paid off. There was a marked reduction in the draw from Oahu aquifer and the water table stabilised. To deal with Oahu's growing population; the Board built water reservoirs, laid larger and better pipes and made sure the city's pumping stations were in the top shape. They also look at new sources of water for the city. Just before the outbreak of World War 2, they began to develop their first facility outside the city, a new station in Halawa Valley which is currently the largest underground water pumping station in Oahu called the Halawa Shaft.
The earth's population continues to grow and freshwater supplies are under threat. In the century between 1950 and 2050, the amount of water available per person is expected to decline by 74%. To combat a global water crisis, nations are inventing new technologies and strategies to deal with water shortages. They are using science and ingenuity to create new water sources and to recycle their existing water. Oahu is currently recycling its water and is producing up to 12 million gallons of recycled water per day. They produce 2 grades of water, one for irrigation and the other for industry. The recycled water is delivered to users through pipes separate from the drinking water distribution system. Though safe for human contact, recycled water is not intended for drinking. Recycled water is regulated by the State Department of Health to the highest level of safety. However, they estimated that the current water supply system cannot sustain the future demand and eventually they will have to deal with desaltation of the sea water. The Board of Water Supply is also active in engaging the community. They had a far ranging series of programs to teach the residents all about water and how to preserve and protect their precious water supply. They also work with other agencies to safeguard the environment and the health of the water users. And above all, despite of all this advance and complex system, the water in Hawaii only cost $2.25/gallon!!!
Source: Board of Water Supply (2007) Water for Life. Honolulu: Honolulu Board of Water Supply (25M/07).
