Underground water reserves in around 9 out of every 10 Chinese cities are polluted or overexploited, and could take hundreds of years to recover, the official Xinhua news agency reported on Saturday. In coastal areas overuse of reservoirs is allowing saline seawater to seep into and contaminate freshwater, while underground pressure changes caused by depleted reserves are also causing massive subsidence nationwide. China has limited water resources, less than one third of the global per capita average and falling. Groundwater is crucial because it provides up to 70% of drinking water. "Groundwater is now contaminated in about 90% of the nation's cities,' Xinhua quoted Zhang Lijun, deputy director of the State Environmental Protection Administration saying.