On Peru's coast, virtually every city has its eye on an uphill neighbor's water supply. In neighboring Bolivia, street protests in 2000 and 2004 known as the "water wars" forced two private companies, Bechtel and Suez, to give up water management concessions. City planners in Quito, Ecuador's capital, are looking to the Amazon to replace water supplied by dwindling glaciers. And Brazil plans to meet its growing energy needs by damming rivers throughout the Amazon, which critics say could further disrupt the region's hydrology.
The Intergovernmental Panel on Climate Change predicts that by 2020 upwards of 1.5 billion people worldwide will be facing water stress, including anywhere from 7 million to 77 million in Latin America.
"Inherent in these projections," said IPCC Chairman Rajendra Pachauri, "is the potential for conflicts and the disruption of peace."
With nearly 9 million people, Lima, Peru's capital, is the second-largest desert city in the world, after Cairo. It grew up beside a river that slices down from the Andean highlands to the Pacific Ocean. Many such coastal valleys contain vestiges of pre-Hispanic canals and irrigation systems, a sign that water management has been a challenge for several millennia.
"Lima is a thirsty city," says Guillermo León, president of the board of directors of the state-run water and sanitation company, SEDAPAL. In shantytowns lacking water hookups, residents must buy water from tank trucks. They use less than one-third the amount of water used by residents of wealthier districts, but pay four or five times as much for the water.
Water stress is also serious on the Bolivian Altiplano, the two-mile-high plain near Lake Titicaca, an area that is home to more than 3 million people. That region's rivers provide an average of 132,000 gallons of water per person per year – scarcely enough for household use, even if Bolivians are thriftier than US families, who can use up to 400 gallons a day, according to the U.S. Environmental Protection Agency.
Often, the scant water available is polluted. Three-quarters of wastewater in Peru is dumped untreated into rivers, lakes and the Pacific Ocean, and the Health Ministry has identified dozens of rivers polluted with lead, cadmium, arsenic, mercury and other metals from mining operations.
In the Andes, these problems are exacerbated by demand for water for irrigation. About 80 percent of Peru's water goes to agriculture, and only 8 percent of farm land uses water-conserving systems like drip irrigation, according to Abelardo de la Torre, head of the new National Water Authority, which is overseeing the design of watershed management plans throughout the country.
The need for efficient irrigation will become critical within the next few decades, as ice caps disappear from the Andes, where most of the world's tropical glaciers are located, and where small farmers depend on meltwater during the dry season.
Outside La Paz, Bolivia, the Chacaltaya glacier, once billed as the world's highest ski resort, is nearly gone. And Ecuador plans to pipe water from the eastern side of the Andes to supplement the dwindling supply from two receding glaciers that provide Quito's drinking water.
In 1991, tropical Andean glaciers covered some 1,065 square miles, with 70 percent in Peru, 20 percent in Bolivia, and the rest in Ecuador, Colombia and Venezuela. Since then, glaciers have disappeared from Venezuela and are shrinking in the other countries. Calculations show a loss of nearly 10 percent per decade.
Ironically, the increased melting means a water bonanza now, but César Portocarrero, an engineer who helps small farmers install drip irrigation systems in Peru's Cordillera Blanca, named for its snow-capped peaks, said he has seen an increase in conflicts between neighbors and communities, which may be an early sign of water stress.