All known forms of life depend on water. It is the single most important substance on Earth. Covering 71 per cent of the Earth's surface, water is plentiful. But the seemingly boundless ocean has been transformed into a global storeroom, mine and rubbish dump. Some regions are now receiving too much rain, while others are receiving too little. 1.2 billion people lack access to a safe water supply, the amount of drinking water available is shrinking and the growth in demand for fresh water is increasing relentlessly. We are approaching a global water emergency. But how did we get into this situation, and what can we do about it? Julian Caldecott reveals where the water we use comes from, and at what social and environmental cost. He explains the history, science, economics and politics behind the looming water crisis, and reveals what the future holds, and what we can all do to make a difference.