When it won the right to host the Olympics in 2001, Beijing promised that it would be treating 90 percent of the 2.78 million cubic metres of waste water produced every day in the city and recycling half of the resultant effluent.

After a 10 billion yuan (US$1.34 billion) investment in the city's sewerage system over the last decade, the commitment on water treatment was surpassed last year and officials are certain the second target will be met when another new treatment centre starts functioning in December.

"In 2006, we recycled 46 percent of the treated water," Wang Hongchen, chief engineer of the Beijing Drainage Group, told a news conference at the Qinghe plant.

"With the new Beixiaohe water reclamation plant coming on line by the end of the year, we will certainly meet our target."

Wang said the 360 million cubic metres of recycled water now produced every year was providing 10 percent of the city's water supply -- an important contribution to a city now in its eighth year of drought.

Recycled water was mainly used for industrial and agricultural purposes, Wang said, but some would fill the huge lake that forms the centrepiece of the Olympic Green, home to most of the Games venues.

Wang said better-quality recycled water would be used at the lake's southern end, where more people would be around, to avoid anyone becoming ill if they were to fall in.

The high cost of recycling -- 1.5 yuan per cubic metre for the better-quality water -- would prohibit much more than 50 percent of the processed water being reclaimed, Wang said.