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.