604One of the world’s biggest cities is running out of water. Sao Paulo, a city of 20 million people, could run dry within weeks. The humanitarian and economic cost would be immense. The fiasco should be a global wake-up call for other metropolises. The immediate cause of the crisis is a year-long drought. The Cantareira reservoir system that supplies around a third of the city’s population is so low that Sabesp, the local utility, has to dip into and treat sediment-heavy supplies and pipe water in from other sources. More