Age: It looks like any other giant building site, a phalanx of multi-storey cranes and an emerging skeleton of steel deep inside the unbearably smelly Beckton sewage works in east London. But by this time next year, what is euphemistically known as the Thames Gateway will rumble into action, using reverse osmosis technology to suck 150 million litres of brackish river water into its innards and disgorge it clean of salt to provide drinking water for close to 900,000 people a day. It …