Water is essential for all life on earth. About three billion years ago life began as small microscopic marine organisms. Nearly 300 million years ago primitive amphibians crawled out of their watery home on to dry land. Humans appeared about 1 million years ago. Since then our numbers have grown enormously and our way of life has had profound consequences for the water cycle, particularly in urban areas.
The water cycle begins with water being evaporated by the sun mainly from the sea, which becomes vapour and forms into clouds. Some of the cloudy vapour blows inland where it falls as rain before eventually flowing back to the sea.
Where does the rain go?
||interception by plant leaves||15%|
|transpiration and evaporation||60%||10%|
|percolation to water table and ground water||10%|