India, April 19 -- It feels like one of our best-kept secrets. The water is running out. And yet we don't seem very worried. Perhaps one reason is that there seems to be so much of it. To put that in perspective, less than 3% of the water on Earth is freshwater. Earth's natural desalination programme, the rains, turns some of the vast ocean stores into potable supply, but we force most of that into drains and oceans, by blocking natural aquifers, filling up lakes and wetlands, and encroaching on rivers. Then the battles begin. Countries spar over dams, regions battle over rivers. In Mexico, drought-stricken farmers have set fire to government buildings and ambushed soldiers, to prevent water from being diverted to the US. Violent clashes be...