Agenda Explainer: Water insecurity

Wherever human beings travel they need water to survive – even on the moon. And the news to raise the hopes of would-be lunar settlers is that there's water even there. But down here on earth there are all too many water-related problems to be solved: not enough in one country – too much in another, water theft and especially poor sanitation. So just what is the true scale of the problem? Stephen Cole explains.