Mexico Shows World Water Forum What Not to Do

With the dry season in full swing Juan María Bautista rarely strays far from her tap in case the water comes in and she can fill the plastic drums lined up in front of her rickety house in eastern Mexico City. "We don't want to ask for what doesn't exist," says Mrs Bautista, who sometimes makes do with an hour of water every seven days. "But it would be nice to have water twice a week."

Tomorrow hundreds of delegates from around the world will gather in Mexico's capital for the fourth World Water Forum, aimed at tackling the global water emergency. But if delegates venture outside the conference hall into the vast metropolis of 20 million people, they will find a vicious circle of acute water problems that is hardly a model to follow.

The mistake goes back 500 years to when the Spanish conquered the floating Aztec city of Tenochtitlan, built in the centre of a lake in the Valley of Mexico, and decided to build their new capital on dry ground. Draining the lakes, an extraordinary feat, laid the foundations for Mexico City's modern day problems.

Mexico City sank around 30ft over the last century, leaving many 16th century churches and modern homes lopsided. With the surface water sources drained out of the valley, it has relied on its underground reservoir to supply a mushrooming population. As the water is sucked out, the spongy lake bed collapses.

The downward lurch is a major strain on the below-ground infrastructure, prompting concern about contamination from cracked drains as well as 35% wastage from the clean water distribution pipes, only upping the pressure to pump more. And there is never enough, with millions within the metropolitan area, about twice the size of Greater London, not even hooked up to the network and tensions rising as a result.

"There is a significant increase in the number and intensity of water-related conflicts," says Manuel Perló of the National Autonomous University, who warns these could escalate into a "water war".

But the sinking, the shortages and the conflicts pale in comparison with the prospect of catastrophic flooding New Orleans-style. Mexico City's lakes may be long gone but the rain still pours down for six months of the year with nowhere to go but a creaking drainage system that pumps it out of the valley. A system breakdown could leave the city waist-high in waste water in hours, which is why the authorities last month announced a $2bn investment programme focused on improving drainage efficiency.

Some critics believe the plan will not do enough. Jesús Campos, deputy head of the National Water Commission, says it will be difficult to present Mexico City as an example to follow during the World Water Forum. "There are a lot of things we can teach other countries ... we can teach them what not to do."