If we have the water, we can probably grow the food – or at least we can if we are able to persuade people to eat rather less meat. Without fresh water we can’t. Water is the pinch point. A quarter of the world’s population does not have enough water for their daily needs. Some large cities have come close to switching off the taps altogether: Cape Town and Chennai, for example. Agriculture in the Murray-Darling River Basin in Australia has been devastated by water mismanagement. Infamously, the Aral Sea – which lies between Kazakhstan and Uzbekistan – has shrunk…