The study lists 20 big cities, which, unless major steps are taken, will "suffer from perennial water shortage because of the demographic growth and climate change" by 2050.
Topping the list for Latin America are Mexico City and Caracas, and Asia's most troubled cities include Beijing, New Delhi, Mumbai, Shenyang, Manila, Bangalore and Calcutta, while Lagos, Abidjan and Johannesburg are facing the biggest challenge in Africa, according to the study.
"China and India are urbanizing very quickly, and they make the challenge bigger. Although China already has done a lot to address the water problem, it has to do a lot more," Revenga told Xinhua.
Revenga said all large cities in the study have to not only improve the availability and distribution of clean drinking water, but look much more at how to restructure water use by agriculture and industry, the two biggest users of water worldwide.
The two experts called on governments around the world to step up efforts in building new infrastructure to improve the access and distribution of water to its citizens.
Moreover, they said governments should launch education campaigns to prevent water waste and enhance conservation efforts to collect and preserve water from seasonal rainfall.
"One study estimated the world will have to spend 180 billion U.S. dollars a year to meet its urban water needs," McDonald said. "Whatever the real figure is, there's a serious issue here the world needs to pay attention to."
