Famine is caused by drought. By far the biggest use to which water is put is agriculture. Between 70 and 80 per cent of the water withdrawn globally is used to irrigate fields. But irrigation is typically fantastically wasteful. It is estimated that only 40 per cent or so of all irrigation water gets to where it is needed.
Most farmers use traditional, very inefficient, methods of irrigation.
Modern methods such as drip irrigation deliver water exactly where it is needed, and in exactly the right amount. Over-irrigation is not only wasteful but potentially damaging for the soil. If soil becomes waterlogged and the water table rises, salts from deep in the ground are carried to the surface, where they can form a crust when the water evaporates. The casualties of mismanagement of water are not always humans. Ecosystems have seldom been accorded any rights to water allocation, and have suffered tremendously from draining, redirection or pollution of waterways for human use.