Construction began yesterday on the Qingcaosha Headwaters project, which is expected to become Shanghai's largest source of raw water.

The plant, which is expected to be operational by 2010, would provide tap water to nearly half the city. The water is to be drawn from the Yangtze River.

Located along an estuary of the Yangtze River northwest of Changxing Island, the project includes a 70-sq-km reservoir. The reservoir will be able to store up to 435 million cu m of water at any one time.

The raw water sourced from the Yangtze River will flow through the pipeline from the Qingcaosha site to 12 tap water plants and seven pumping stations in the city.

After being processed, the water will be supplied to more than 10 million Shanghai residents, about half the city's population.

The Qingcaosha headwaters project will have a daily capacity of 7.19 million cu m of water, all of it for downtown Shanghai, Pudong, Nanhui District and parts of Baoshan, Putuo, Chongming, Qingpu and Minhang districts, said Lu Xiaoru, general manager of Shanghai Qingcaosha Raw Water Engineering Co Ltd.

Although the local water authority has not said how much the project will cost, media reports have estimated that the municipal government spent some 16 billion yuan ($2.09 billion).

It is commonly believed that raw water sourced from the Yangtze River is much cleaner than the city's current biggest water source - the Huangpu River.

Gu Jinshan, deputy director of the Shanghai water affairs bureau, told China Daily that the upper reaches of the Huangpu River now account for about 80 percent of the city's water supply.