Only 3 per cent of the world's water is freshwater and about one third of that is inaccessible. The rest is very unevenly distributed, parts of Canada and the Amazon, for example are both more than amply suppied. Terrible and permanent water stress can be seen, among other places, in the drylands of Africa caused not just by drought, but by poverty leading to poor land management and over-population.;As with so many other things, those most badly affected are the poor nations of the world who are frequently faced with an impossible dilemma: they must either limit their water use to...