"Black slicks" are haunting Liu Shengji and his family since they learned that more than half of the rivers in their province were covered by the slick. Can they drink the water?

"We feel increasingly insecure about the drinking water," said the 42-year-old resident of the capital of Taiyuan, Shanxi Province.

He has reason to be concerned because of river pollution in other parts of China, including the recent chemical leak into the Songhua River in Northeast China and a leak in the Beijiang River in the south.

Shanxi's environmental watchdog agency says 58 of the provinces's 99 rivers were seriously contaminated. It said that the water of only nine rivers were up to Grade I or II of the national standard, accounting for less than one tenth of all rivers in the province.

The river pollution was not limited to Shanxi. In 2005, a series of water pollution incidents wracked unprecedented havoc.

A recent official report said that China's longest river, the Yangtze, is threatened by 28 billion tons of polluted water.

This year China's water pollution problem was underscored by huge spills into the Songhua River of about 100 tons of cancer-causing nitro-benzene chemicals following an explosion at a chemical plant.

"Water is the origin of life and the core of the environment. Water safety is what constitutes people's basic living conditions, not a luxury," said Feng Guangzhi, president of the China Irrigation Districts' Association.

"The vicious cycle, including tainted water sources, polluted drinking water and unclean food, is a vital issue affecting people's health and safety," said He Shaoling, vice chief engineer of the China Institute of Water Resources and Hydropower Research.

Many farmlands in the Yellow River region have been irrigated with polluted water, harming residents' health. Estimates place the cost of health problems and environment problems at 2.2 to 2.7 billion yuan (up to US$330 million) every year.

Water pollution has caused major economic losses. The pollution in the Yellow River has increased the cost of water for industrial use and degraded product quality.

The World Bank said water and air pollution have caused losses equivalent to 8 percent of China's annual GDP. Pollution has contributed to making china's development costs 7 percent higher than the world average.