This is a good time to learn from past experience of always developing new water sources after having polluted the current ones.

Before the 1980s, the main water supply was Suzhou Creek that passes through the city center.

The creek became so polluted and smelly that the city was forced to turn to the Huangpu River for water.

As industries developed, however, more polluting waste was poured into the Huangpu River, resulting in poor water quality. Now the city is considering finding another major resource for its water.

While this is indeed a solution, it is not a sustainable way to improve the city's water supply, as Li Jianhua observed.

Improving the eco-environment of the Huangpu River is of even more importance.

The water in the Huangpu River originates from Tai Lake (70 percent) and Dianshan Lake, in neighboring provinces.

The water quality at its origin is about the same as that of the Yangtze River. It is considered Grade III in the national standard for water quality, meaning it's drinkable after processing.

Yet it deteriorates as it flows toward the Huangpu River and degrades to Grade IV, which is below the national standard for potable water after processing.

Worse, "Some indicators of the water drawn from the Huangpu River fall into Grade V during the low-water period in winter or early spring," said Li. Grade V is the lowest quality, meaning it is only safe for agricultural use after processing.

This is the result of all kinds of industrial and agricultural pollution along the lakes.

For example, in Zhejiang and Jiangsu Provinces, many small chemical factories on the banks of the Tai Lake discharge waste water into the river without proper treatment, causing all kinds of water crises.

In the part of Tai Lake in Wuxi, Jiangsu Province, for instance, the outbreaks of blue-green algae due to industrial pollution in recent years are a serious threat to the normal water supply of Wuxi and also cities on the lower reach of the river.

The water supply in Yancheng city in Jiangsu Province has been disrupted since February 20 due to pollution released by a local industrial factory into the city's main water source.

Shanghai is also the victim of such pollution as it is situated at the lower reach of the Tai Lake. But Shanghai itself also produces pollution, primarily from aquaculture and poultry excrement, as both Li and Zhu Jianrong pointed out.

For example, Dalian Lake in Qingpu District, from which the water flows from Dianshan Lake towards Huangpu River, is now threatened by eutrophication from excessive use of fish food. That means there's a buildup of organic and mineral substances that choke out oxygen and lead to proliferation of unwanted plant life, such as algae.

Originally a wetland that could purify itself, the lake is now endangered after being broken up by farmers into numerous small fish ponds.

Fortunately, the government is taking steps to restore Dalian Lake and its surrounding wetlands into a natural, self-purifying ecosystem that attracts birds.

(Shanghai Daily February 27, 2009)