Water crisis as Mexico City sinks faster than Venice

Perhaps nowhere is the physical evidence of overpopulation's effects as obvious as in Mexico City. When it was the capital of the Aztec empire, it was set on a broad inland lagoon. Today, not only is the lake dried up, but the city is pumping water from its underground aquifers so fast that the whole city is sinking by a foot a year.

Mexico City's underlying aquifer is now collapsing at a staggering rate beneath the streets. While Venice slips into the Adriatic at a fraction of an inch each year, Mexico City is lurching downwards by as much as a foot a year in some areas. Over the past century, it has dropped 30ft.

Chugging the equivalent of one Olympic-sized swimming pool full of water every minute, the city's strained aquifers are dragging much of the capital's rich heritage down with them, while the 20 million residents face problems that include water-borne diseases, power outages and the threat of riots.

The result of a head-on collision between booming demand and finite resources, Mexico City provides a sneak preview of a situation that the United Nations warns could become widespread in coming decades as the world's mega-cities continue to grow unchecked and unplanned. Unesco claims that up to seven billion people from 60 countries could suffer water shortages by 2050. ...

The first strains began to show with massive migration in the 1940s; the capital began swallowing up one satellite town after another as it grew by 7 per cent a year. Faced with shortfalls as the underlying sand and clay aquifers failed to keep pace with demand, city authorities tapped into two neighbouring river systems at a massive cost.

The city now has five pumping stations working around the clock to draw water vertically three-quarters of a mile from the neighbouring Cutzamala River basin and from the lower catchment area of the River Lerma. Paying about $50,000 (£28,000) a day in water rights alone, the system consumes the same amount of electricity as Puebla, a city of 1.3 million people to the south-east.

Now comprising 350 neighbourhoods packed into a smog-wreathed metropolitan area more than twice the size of greater London, the city swills a massive 10.5 million gallons of water each day.

Used by residentsand by water-intensive industries such as beer brewing and soft-drink bottling, the ever-expanding metropolis's supplies are again running short. ...

Below street level, the ongoing subsidence is wreaking havoc with the water distribution and drainage systems. The city's 8,300-mile network of water pipes routinely fracture, losing up to 40 per cent of potable water supplies, according to some estimates. The city's sewage used to drain away by gravity towards a far-off outflow in the Gulf of Mexico but now needs to be first pumped uphill before it can be drained.