It’s hot. Very hot. And as ever in the UK when the sun comes out for more than a few, fleeting summer afternoons, there is talk of water shortages, rationing and hosepipe bans. It is a pity the millionaire bosses of privatised water companies do not spend more time lining leaking pipes and less time lining their pockets. Yet despite this and other controversies over charges, metering, mismanagement of upland catchment areas and periodic downstream flooding, Britain’s water politics are relatively benign. Not so in many other parts of a densely populated world, where the availability of clean, potable water, and water for agricultural and industrial use is a hot political, security and economic issue – as well as a frequently unmet, basic human need. Ethiopia’s stupendous $4bn (£3bn) Grand Renaissance dam on the Blue Nile is a case in point. When completed, it will be the largest dam in Africa, generating more than three times the energy produced by the Hoover dam in the US. But for some, it is a cause for war.