Unlike most of the resources we consume such as oil, rice and steel, there is no alternative for water – it is the only natural resource with no substitute. Today over 6 billion people share the same volume of water that 1.6 billion did a hundred years ago. Although two thirds of the earth’s surface is water, only 3% per cent of this is fresh water and, if you deduct the majority share that is locked up in the polar ice-caps and other glaciers, we only actually have access to around 0.5%.