Hanoi  - The unplanned exploitation and poor management of underground water are leading to a fast fall in its levels in Vietnam, government officials said Monday.

Do Tien Hung, director of the Centre for Water Resources Planning and Investigation, said "some negative impacts have appeared" from the falling water levels.

Residents of some towns are finding it harder to extract underground water and land has subsided between a half-metre and 1 metre due to the loss of pressure after underground water has been overexploited, Hung said.

Nguyen Thi Ha, director of the Centre for Water Resource Observation and Forecast, said underground water levels had fallen by 6 metres in Hanoi and 10 metres in Ho Chi Minh City in the past 10 years in some areas.

Nguyen Van Minh, a well driller in the Soc Son district of Hanoi, said many families were asking him to redrill their wells because they had run out of water.

"To get underground water, we have to dig 80 metres deep instead of 60 metres as before," Minh said.

Vietnamese laws regulate well drilling by asking people to get permission from authorities before boring, but the law is widely ignored.

In the Mekong Delta, thousands of wells have been drilled for shrimp-breeding lagoons and fields, but the local authorities have failed to control them.

Besides the fast drop of underground water levels, the quality of underground water is worsening.

"The colour of water has changed," Minh said. "Ten years ago, water was clear and quite clean, but now it becomes yellow and saltier."

The online Vietnamnet newspaper quoted Ho Chi Minh City's Department for Environment as saying tests conducted in 2008 revealed 81 per cent of the water samples did not meet standards for pH and dissolved solid substances. The content of toxic chemicals in underground water increased substantially, particularly nitrate and ammonia, it said.

Testing results in the first three months of 2009 in Ho Chi Minh City showed that the water level and quality of underground water was becoming worse in some areas. The content of bacteria and toxic chemicals rose, and in some places, the water was tainted with alum or saltwater.

To protect underground water, the Vietnamese government is asking for help from many countries.

On Thursday the German government pledged 1.16 million dollars to finance a programme to help Vietnam improve ground water management. The programme was scheduled to run until 2013.(dpa)