Up to a twentieth of all the water pumped through Moscow's pipes and sewers gushes out through ruptures into the soil, undermining the foundations of thousands of buildings and polluting lower-level fresh water supplies, geologists say.


Massive leaks in the city's water and sewage pipes amount to almost 10 million cubic meters of water a day, or 5 percent of all water running through the city's pipes, said Dmitry Yefremov, deputy director of the Moscow geological center, or Geotsentr.


The leakages, combined with poor drainage, have raised the water table above the critical level of 3 meters below the surface in 40 percent of the city, he said.


Careless Soviet-era construction dammed up underground rivers, removed whole hills and disturbed natural drainage, leaving the city with a topsoil incapable of absorbing the huge supply of water, said Yefremov.


The high level of groundwater floods basements, erodes foundations and provides a fertile breeding ground for mosquitos, said Sergei Petrenko, in charge of monitoring Moscow's soil at the Geotsentr. Sometimes its effects can be calamitous.


"It can pull down buildings," Pet-renko said in an interview. "It can happen suddenly, literally in a few hours."


Simultaneously with the rise of groundwater higher up, heavy use of clean water at a much greater depth is causing fast seepage through a middle layer of limestone, Petrenko said. Polluted groundwater pours down through this layer, which erodes and collapses in parts, causing similar subsidence at ground level.


Several apartment buildings have collapsed in recent years, mostly in the neighborhood near Khoroshevskoye Shosse, he said.


Petrenko said the danger in that neighborhood had lessened, after local factories were ordered to stop pumping out deep-level water and to use water from the Moskva River instead.


But even with the curtailment of pumping, polluted water is still seeping down into the low-level clean water supply, Yefremov said.


Although the geologists have drawn up a map of regions where buildings are at risk, with the northern and northeastern parts of the city marked as most prone to erosion and sinking at a rate of 1 to 2 millimeters per year, they said there were no particular buildings about to collapse.


Major leakages could cause sudden subsidence in these regions, but most apartment buildings are quite new and would withstand shifts in the ground for some time, Yefremov said, adding: "We have it under control."


But Mikhail Orlov, who teaches hydrogeology at Moscow State University, said that the surveys were not widespread enough to guarantee safety.


"You can't say that there is no danger. We don't know where these unpleasant phenomena occur," he said.


Although many major cities in Europe face the same problem, the leakages in Moscow are far more serious than elsewhere, Orlov said. In some parts of the city 35 percent of all piped water leaks away. If this happens in a region at risk, the ground could collapse suddenly, Orlov said.


Orlov said that his own office, in the university's Stalinist tower on the Sparrow Hills, is sinking 2 to 3 millimeters a year because of heavy leaks.


In 1992, Petrenko and other geologists urged the city to change construction plans, improve drainage and reduce pipe leakagess. Construction is now done more carefully and with geological studies, but the city's pipes are only replaced piecemeal because of a lack of funds, Yefremov said.


Orlov said that many architects and construction firms still use outdated regulations and repeat the same mistakes made in the Soviet era. Recently, Orlov said, the opening of the Altufyevskoye metro was delayed because high groundwater had caused the walls to cave in.