Another world
"Climate change is going to affect water levels in the mountains and reduce the flow of rivers," said Antonio Ioris, a professor of geography at Cardiff University in Wales.
But he said dwindling water reserves are not the main problem, insisting that poor people's tenuous access to water is very low on policymakers' list of priorities.
"The situation on the outskirts of Lima stems not only from a lack of urban planning but also from problems in rural areas that force people to migrate to the city," said Ioris, who specializes in the link between population and environmental issues in Latin America.
Along dirt roads in some areas of San Juan de Miraflores, concrete staircases lead to spots that are even harder to access and cannot be reached by the trucks that bring in water.
So these people get by the best they can, and on average pay six times what people connected to the utility grid pay for water, the government says.
In one hilltop area of San Juan de Miraflores, a water drum blocks the last step of a staircase heading up toward another world.
Up on the peak, a two-meter high, 10-kilometer long (two-yard high, six-mile long) concrete barrier -- people call it the "wall of shame" -- separates San Juan de Miraflores from a rich area on the other side. The idea is to keep poor people out.
Through cracks in the wall one can see the lush vegetation of Santiago de Surco, a Lima neighborhood with one of the highest rates of water consumption -- 200 liters per day per person, according to Sedapal.
There on the other side, thick green grass is fed with drinking water and people rest under leafy trees.
"Surco seems like another world," said Cristel Mejia, who runs a soup kitchen on the poor side of the wall.