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I’M STANDING in a festering slum: there are no sewers, no drains, the
communal pit latrines are overflowing, and the alleyways are too narrow for
conventional latrine-emptying trucks. Three-quarters of a million people are
trapped in this area of about 100 hectares—roughly the size of London’s
Regent’s Park. For the inhabitants, clearing the sewage is a pressing
priority.

“It’s the kind of practical problem aid agencies are not very good at,”
Graham Alabaster who is based in Nairobi with Habitat, the UN’s urban
development agency, tells me. “They are hot on sociology, but not so hot on hard
technology.”…

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