Since the dawn of civilisation humanity has recognised the importance of rainfall as the primary source of water which sustains life. Unlike many of the materials used in the world today, water is a renewable resource. The total quantity of water on the earth is huge and it has been estimated at about 1l-2billion cubic kilometres volume. One way of envisaging this quantity is as water to a uniform depth of 3,000m over the whole surface of the earth.
The ancient practice of irrigation has changed substantially this century; but what is the bottom line?