Sources of water drying up

In addition to pollution, experts say the most pressing problem with groundwater is that levels continue to fall because of overexploitation.

"Land subsidence has hit nearly 100 cities in 16 provinces. The total area of land subsidence across China is more than 90,000 square kilometers," said Gao Cunrong, from the China Institute of Geological Environmental Monitoring.

On the North China Plain alone, the area of land subsidence totals more than 70,000 sq km, and groundwater levels have dropped 100 meters since the 1980s, he said.

Cones of depression were formed by the large-scale exploitation of groundwater. So far, China has more than 100 regional cones of depression, totaling more than 150,000 sq km.

In addition, factories built upstream of water sources have caused pollution. The potential for problems such as this wasn't considered when China started building its groundwater-monitoring network.

Gao said other problems with groundwater are karst collapse - also known as sinkholes - and seawater intrusion "Industrial pollution is the most serious of all types of pollution. It mainly takes place at industrial parks and therefore does not affect a large area," he said.

"However, government monitoring of industrial pollution is very weak in China, because only a small number of monitoring wells have been constructed at industrial parks."

Chen Ming, from the Ministry of Water Resources, said 108.4 billion cubic meters of the total 123 billion cu m of exploitable shallow groundwater were consumed nationwide in 2011.

"Our plan is to keep consumption below 93.3 billion cubic meters, and completely eliminate the use of deep groundwater in some areas by replacing it with a greater supply of surface water," he said.