A report by the World Economic Forum, which runs the annual Davos meetings of the international business and financial elite, says that lack of water, will "soon tear into various parts of the global economic system" and "start to emerge as a headline geopolitical issue".
60 per cent of China's 669 cities are already short of water.
The World Water Development Report, compiled by 24 UN agencies under the auspices of Unesco, adds that shortages are already beginning to constrain economic growth in areas as diverse and California, China, Australia, India and Indonesia.
The report also expects water conflicts to break out in the Middle East, Haiti, Sri Lanka, Colombia and other countries.
"Conflicts about water can occur at all scales," it warns. "Hydrological shocks" brought about by climate change are likely to "increase the risk of major national and international security threats".