SHANGHAI: Floodwater sluiced from nearby rivers is introducing pollutants into Shanghai's water resources, but tap water in the city remains safe.

Shanghai Water Authority said yesterday that a high content of harmful substances - ammonia, azote and nitrite - has been detected at the intake spots of Shanghai's two reservoirs on the Yangtze and Huangpu rivers.

The pollution is caused by floodwater sluiced from nearby rivers. The city's drinking water remains safe due to carefully choosing the intake times from the reservoirs and increased levels of water sanitation.

The Shanghai water authority said it has been closely monitoring the water quality in nearby water channels, especially following the onset of flood season and the outbreak of blue-green algae in Taihu Lake. The growth of algae shut down the city of Wuxi's drinking water supply for a week.

Continuous downpours, which started last month, have brought floods, landslides and death to several provinces.

Liuhe River in Jiangsu Province, with floodwater from Taihu Lake and other water channels from Suzhou, has been pouring large amounts of polluted water into the part of Yangtze River near Shanghai.

A sampling on Tuesday at the intake spot of Chenhang Reservoir, which is 4 km from the Liuhe and Yangtze rivers, found the ammonia and azote content more than 20 times higher than usual but still within acceptable standards. The Chenhang Reservoir contributes one-third of the city's water supply.

The other reservoir in the upper reaches of Huangpu River, also connected to Taihu Lake, was also found to have nitrite higher than standard at its intake spot. The nitrate is mainly from agricultural and industrial waste dumped in nearby rivers, according to an expert quoted by Shanghai Morning Post.

To safeguard Shanghai's tap water, city water companies have adjusted their intake hours to avoid low tide, when pollution is comparatively higher. They have also extended the chemical precipitation period and added chemicals when necessary.

(China Daily 07/12/2007 page4)