China's major cities rely heavily on water collected in catchment areas that are under threat from encroachment and pollution, according to a new report from The Nature Conservancy, a leading global conservation organization.

The report, which was released on Monday, said Beijing, Shanghai and 28 other major cities depend on surface water for daily consumption, but it noted that 73 percent of the water catchment areas that supply that surface water were impacted by medium to high pollution levels.

The nation's 30 largest and fastest growing cities have seen a surge in demand for water because of their rapid expansion, and they now consume around 29.6 billion cubic meters of water annually, the report said.