The majority of China's underground water is of poor quality, with 80.2 percent unfit to drink, a government report recently revealed.

80% underground water undrinkable in China.[File photo]

Pollution and overexploitation are posing major threats to water resources, said a monthly report from the Ministry of Water Resources.

Last year, the ministry conducted a survey of 2,103 water wells in the northeast, north, northwest, and central parts of China. It classified water resources into five categories, Class I being the best and Class V being the worst.

The ministry found that no water sources were up to the standards of Class I, while 19.9 percent were classified as Class II and Class III. Water in the last two categories, which are unfit for human consumption, accounted for 32.9 percent and 47.3 percent, respectively.

Ammonia, nitrites, and nitrates are the major pollutants, while heavy metals and toxic organic compounds were also found in some areas.

The report also revealed that China's underground water has been over-extracted. In January 2016, underground water reserves in China's major plains decreased by 8.24 billion cubic meters (approximately 8.24 billion tons)?from a year ago.

Previous statistics from the Ministry of Land and Resources show that nearly 70 percent of Chinese people drink water from underground sources.

"In Chinese cities, drinking water often comes from deep underground sources, which are not easily polluted, but in the countryside, people often drink shallow underground water where pollution has a bigger impact," said Ma Jun, head of the Beijing-based Institute of Public and Environmental Affairs.

Treating polluted underground water is very difficult, Ma said. He also warned that overexploitation might result in secondary disasters like rock fractures and caves-in.