The country’s water woes were thrown into the spotlight this week with the release of government statistics and reports showing the powerful impact on the nation’s ecosystem of two decades of rapid economic growth.

"When you want economic growth, there are a lot of things you don’t pay attention to," said Kenneth Leung, an ecotoxicologist from the University of Hong Kong. "This is a trade-off."

China’s environmental bureau said on Wednesday that underground water in 90 percent of Chinese cities was polluted and that the situation was getting worse.

The pollution is generally caused by industrial waste from factories or untreated human waste discharged into rivers and then seeping into the ground.

In a report on Wednesday, Xinhua news agency quoted E Jingping, vice minister of water resources, as saying about 300 million Chinese rural residents, or one-third of the total rural population, drink unsafe water.

Previous government reports have said more than 70 percent of China’s rivers and lakes are polluted, while about 400 of China’s 600 largest cities suffer from water shortages.

Environmental experts warn the pollution of China’s rivers, lakes and wetlands has a knock-on effect as it contaminates underground water, which China’s cities are becoming more reliant on for drinking needs.

This increasing reliance has led to an over-exploitation of ground water, which in turn exacerbates the pollution, they say.

Meanwhile two large industrial toxic spills in China’s rivers in as many months have forced authorities to launch major cleanup campaigns and cut the drinking water supply to millions of people over health fears.

Underground water resources are being overtapped at unsustainable levels in 164 regions, covering some 190,000 square kilometers (76,000 square miles) largely in the north, according to earlier state reports.

Scientists said the over exploitation has caused polluted surface water to seep into aquifers, or underground reservoirs, and contaminate underground water that is normally a clean source of drinking water.

"After the ground water has run out ... surface water is more easily seeped into it," Ma Jun, a Beijing-based independent environmental consultant, said.

"So this has become a vicious cycle."

Unscientific treatment of industrial and urban waste as well as unsafe disposal are also to blame, according to Zhao Zhangyuan, a retired expert from the Chinese Environmental Science Research Institute.

"The biggest ‘cancers’ are urban landfills, petrol stations and industrial and agricultural effluent," he wrote in a recent article.

Landfill sites should be well-lined to ensure that there is no leakage into the nearby ground water sources but Zhang said much of China’s waste, some 72 billion tons, are causing serious contamination at old-style landfills.

"(It is) very difficult to find unpolluted groundwater nowadays," he wrote. "The more economically developed a place is, the more varieties and quantities of poisonous materials it has."

Scientists say the pollution of underground water has seriously threatened drinking water quality.

High levels of heavy metal and nitrates as well as petroleum chemical products and pesticides are found in China’s contaminated underground water in many places, a Beijing-based environmental scientist told AFP.

Exposure to high levels of nitrate in drinking water has been linked to a number of chronic health conditions, including birth defects, cancer and hypertension, the university scientist, who did not want to be named, said.

Underground water is the source of drinking water for nearly 70 percent of China’s population and is the source of some 40 percent of the country’s agricultural irrigation.

The Chinese government has said it intends to improve water quality.

It has allocated more than 18 billion yuan (.17 billion) to build 800,000 drinking water projects in rural areas since 2000, and intends to provide safe drinking water to every rural family by 2020.