Efforts to improve?Shanghai's water quality are being frustrated by decades-old pipes, experts and officials have said.

This comes after it was announced that from next year a water plant in Baoshan District will be able to supply water that can be drunk from the tap, using technology seen in the World Expo 2010.

But Zhu Junxiang, a spokesman for Litre, the company providing the technology to Luojing Water Plant, said the 100,000 residents receiving the new supplies have been advised not to drink the water direct from their taps as it may be contaminated en-route in rusted, scaled pipes.

The hyperfiltration membrane technology in the Luojing plant that was used in drinking fountains at the Expo is to be extended to other local plants, he said.

The city has been investing heavily to improve tap water at the source - such as the 17 billion yuan (US$2.63 billion) Qingcaosha Reservoir on the Yangtze River - and at treatment facilities.

But drinkable tap water remains a dream, mainly because of problems with rusting iron pipes, some of which are more than 20 years.

Shanghai has one of China's longest and most complicated water systems, said Gao Naiyun, director of the Environmental Science and Engineering College of Tongji University.

She said engineers have to add extra chlorine to ensure safety en route to homes, which leaves a chemical smell and makes the water unsuitable to drink from the tap.

Shanghai Vice Mayor Shen Jun has said pipelines and water tanks in local homes will be cleaned to ensure that purer water from the new reservoir does not get polluted.

The city has more than 200 million square meters of old residential houses with pipes that need renovating, said Gu Jinshan, deputy general manager of Shanghai Chengtou Corp, a major utilities company that owns most of the city's water plants.

Gu said the company had begun the work, but it will take several years to complete.

Shanghai Chengtou planned to first complete renovations for the city's rural areas before 2015, an official told Shanghai Daily yesterday.

The company launched a 45-day renovation program in the city early this year.

Engineers repaired many pipes found to have cracks of up to 11 centimeters, Gu said.

Qingcaosha Reservoir began providing water to the city last December and now provides tap water to 10 million Shanghai residents.