Major cities worldwide may face a water shortage crisis by 2050 if relevant governments don't react quickly, experts with a leading environmental group said Monday.

The water shortage will mostly affect basic daily needs such as drinking, cooking, bathing and washing clothes, and the poor residents of the world's major cities in developing countries are the ones who will suffer most, the experts warned.

"By 2050, big cities that will not have enough water available nearby include Beijing, New Delhi, Mexico City, Lagos and Tehran. China and India will be particularly hard hit unless significant new efforts are taken by their cities," Robert McDonald, a scientist with the Washington-based Nature Conservancy, told Xinhua in an interview.

McDonald and Carmen Revenga, another scientist from the Nature Conservancy, are the co-authors of a new study -- "Billions of City Dwellers in Water Shortage by 2050?"

They warned if cities don't increase efforts to resolve the world's growing water crisis, several of the key United Nations Millennium Development Goals (UNMDGs) won't be achieved.

McDonald said more than 1 billion people are likely to suffer chronic water shortage on a daily basis by 2050, while more than 3 billion more will suffer water shortage at least for one month every year.

"Ten years ago we had 1.5 billion people in the world without access to clean drinking water, and today we talk about 800 million, so we have made very good progress on the UN Millennium Goals," McDonald said. However, he warned that this positive trend could easily be reversed.

"The thing I am really worried about is how the poorest cities, which already have trouble delivering clean drinking water to their citizens, are going to be able to afford to get water to their residents. Unless new capital is available for investment, the problem will get worse," McDonald said.

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."