Twice a day, Elena Quispe draws water from a spigot on the dusty fringe of the city, fills three grimy plastic containers and pushes them in a rickety wheelbarrow to the adobe home she shares with her husband and eight children.
But the water supply is in peril. El Alto and its sister city of La Paz, the world's highest capital, depend on glaciers for at least a third of their water -- more than any other urban sprawl. And those glaciers are rapidly melting because of global warming.
Informed of the threat, Quispe, a 37-year-old Aymara Indian, shows alarm on her weathered face.
"Where are we going to get water? Without water how can we live?" she said.
Scientists predict that all the glaciers in the tropical Andes will disappear by mid-century. The implications are dire not just for La Paz-El Alto but also for Quito, Ecuador and Bogota, Colombia. More than 11 million people now live in the burgeoning cities, and El Alto alone is expanding at 5 percent a year.
The melting of the glaciers threatens not just drinking water but also crops and the hydroelectric plants on which these cities rely. The affected countries will need hundreds of millions of dollars to build reservoirs, shore up leaky distribution networks and construct gas or oil-fired plants -- money they simply do not have.
"We're the ones who've contributed the least to global warming and we're getting hit with the biggest bill," lamented Edson Ramirez, a Bolivian hydrologist who coordinates UN, French and Japanese-sponsored projects to quantify the damage exacted on fragile Andes ecosystems by richer nations that use more gas and create more pollution.
Bolivia, South America's poorest country, is responsible for just 0.03 percent of the world's carbon dioxide emissions that scientists blame for global warming, Ramirez said. The US, by contrast, contributes about one quarter.
Bolivian President Evo Morales, in an interview earlier this month, said he would seek legal remedies if rich countries do not agree to pay for the damage they have wreaked on the developing world.
"It's not a question of cooperation. It's an obligation," he said.
UN Secretary-General Ban Ki-moon is urging that a new global treaty on climate change provide funding to help poor countries adapt to its damaging effects. Ban made the recommendation recently when UN scientists released a report saying the 40 leading industrial countries produced 46 percent of global greenhouse gas emissions in 2004.
Starting in 2009, demand for water will outstrip supply in La Paz-El Alto, the government estimates. Without urgent, expensive projects -- only now in initial planning stages -- sustaining even the current population of 1.7 million would be impossible, said Oscar Paz, director of Bolivia's climate change program.
Similar fears are heard in Quito, which gets less than 10 percent of its water directly from the Antizana and Cotopaxi glaciers but much more from the watersheds they feed. The Ecuadorean capital is expected to run short in 2015, even with a battery of projects already under way, including new reservoirs.
So Quitenos plan to cut a US$1.1 billion tunnel through the cordillera and get Amazon basin runoff, said Edgar Ayabaca, director of the city's so-called "Western Rivers" project.
He said work on the tunnel needs to begin by 2010 if supply is to continue to meet demand.