The water crisis silently developing beneath Mexico City is getting harder to ignore.

With the underground aquifer that provides most of the Mexican capital's fresh water drying at an alarming rate, the city is ever more reliant on topping up supply from the dams, pipes, and pumps of the Cutzamala system, more than 60 miles away.

Maintenance work on that system has now temporarily cut off supply for about a quarter of the city's 22 million inhabitants.

"These are very important emergency measures for the city," Ramón Aguirre, head of water management in the city, told reporters. "Everybody should be careful with water. They should wash using a bucket and a bowl."

The cut off started at the stroke of midnight last Wednesday and is due to last until Tuesday morning. The authorities say a full normal service will not be reestablished until next Friday.

Such interruptions in Mexico City's water supply have become a periodic feature of life in the metropolis over the last five years, but this time it is lasting longer than usual.

The federal government has promised there will be fewer breaks once it has finished constructing new pipes in Cutzamala system, which was built in the 1970s. But this does not address the deeper problem that there is no let up in the draining of the aquifer.

Every year the city extracts 1.3 billion cubic meters of water while rainfall, and some injection, only recharges it by 700 million cubic meters. In other words, it is losing water at nearly double the rate at which it is being recharged.