 "Running water would change everything," says Luz Caballero wearily as she stirs a huge pot of beans in the Santa Maria People's Restaurant in Villa El Salvador, a sprawling, dusty shantytown on Lima's southern outskirts. "Living without it is just too hard."  Ms Caballero and the other locals take it in turns to staff the co-operative restaurant, serving up 100 cheap but filling lunches every day. If cooking on this scale seems complicated, then doing so without tapwater takes on an epic quality, with a continuous time-consuming, energy-sapping shuttling of buckets from the plastic barrels in the street outside.  Ms Caballero and her neighbours are among roughly 1.2 million residents of the Peruvian capital without running water. They rely on unregulated private water trucks, which charge up to 30 soles (?6.70) per cubic metre - 20 times what more affluent Peruvians pay for their tapwater - and frequently leave their customers waiting desperately. The new mayor wants to end this exploitation, but she faces immense challenges in a city where climate change has put water sources high in the andes under unprecedented pressure.  Lima receives less than a third of an inch of precipitation a year and relies entirely on andean rainfall and glacier melt, both in serious long-term decline. The R?mac, the largest of the three rivers that feeds the capital, has seen its low season flow fall more than 20 per cent in recent years. Satellite photos of the Eulalia Glacier, which feeds into the R?mac, show it to have shrunk dramatically just in the last decade, due, scientists say, to global warming.  With a population of 8.4 million, Lima is the world's second largest desert city after Cairo. However, while the Nile flows at a rate of 2,830 cubic metres per second, the R?mac averages just 29 cubic metres per second.  Sandwiched between the Pacific and the andes, Lima is trapped in a thermal inversion, making its climate unusually stable and almost entirely preventing rain. The watershed around Marcapomacocha, a system of high-altitude lagoons that supplies Lima with almost half its water through a trans-andean tunnel, has also seen annual precipitation fall by 148mm per decade since it became operative in the 1960s. On current trends, Marcapomacocha could receive no rain at all by the middle of this century. Scientists are researching whether the fall is due to a natural, regional cycle or global climate change.  Peru, with its mountains and rainforest, is actually well-endowed with hydrological resources. But 98 per cent of the andes' run-off, including the source of the amazon river, flows east into the sparsely populated amazon basin, while two-thirds of Peru's 30 million inhabitants live on the arid Pacific coast.  "This mismatch began 500 years ago with the arrival of the Spaniards," says Jos? Salazar, president of the country's urban water regulator, Sunass, noting how the Incas and other pre-Columbian civilisations located their urban centres near water sources in the andes. To be closer to Spain the conquistadors established their capital on the coast: "Today, we are picking up the bill for this colonial legacy."  Many of Lima's poorest residents have now repeated that error by squatting on barren, unstable hills on the city's fringes. The cost of installing pipes and pumping water to their remote, ramshackle homes is often many times higher than in more developed neighbourhoods. Mr Salazar added: "Now the people are there, you can't kick them out, and somehow you have to deal with giving them water."  Villa El Salvador bega 