20 Cities That Need More Water

By Laura Dattaro
Published: June 10, 2014

More than 99 percent of Earth’s bountiful water supply is unfit for drinking. Most of it, 97 percent, is saltwater, with another 2 percent locked up in ice caps and glaciers. Getting the remaining water from its source to the people who need it every day is an increasingly complex task. Now, for the first time, a team of researchers has mapped the water sources of more than 500 cities, finding that cities move 200,000 Olympic swimming pools’ worth of water almost 17,000 miles every day.

The researchers, led by hydrologist Rob McDonald, used computer models to show that about 25 percent of cities use at least 40 percent of their available water, meaning they are under water stress. Previous estimates had the number of water-stressed cities as high as 40 percent.

Some large cities depend on water underground, known as groundwater, and a select few turn the ocean’s salty water into drinkable water, a process called desalination. But the majority of the cities studied, almost 80 percent, largely use surface water — reservoirs, lakes and other water sources on the Earth’s surface, which are more susceptible to immediate changes in weather, like droughts, McDonald said.

“A city like San Antonio that's using groundwater, if there's a two-week drought in San Antonio it doesn't really affect their water supply,” McDonald told “Atlanta is an example of a city that uses surface water, and they don't have a ton of storage, so a short-term drought can get them in some trouble.”

(MORE: California Drought Threatens Food Supply of All Americans)

Ultimately, McDonald said, climate change will affect both sources, as the extremes of wet and dry start to become more intense. Globally, this will be more difficult for poorer cities with fast-growing populations, who don’t have the income to keep up with developing infrastructure. More economically secure cities, like those in China and the United States, have a better capacity to plan for and adapt to climate change. Southern California has arguably the biggest water system in the world, McDonald said, with China building a huge new system to bring water from the south to the north.

“[In California] you do get some big rain events…but the dry season is going to be very dry in California now,” McDonald said. “And so all of those California cities, they either need to have more storage of water or they need to start thinking about other sources.”

The research is published in the open-access journal Global Environmental Change.

This slideshow shows the 20 largest water-stressed cities in the world. The researchers did not rank them, so they are shown in alphabetical order. 

A city is considered water stressed when it is using 40 percent or more of its available water. Click through to see the 20 largest water-stressed cities in the world, in alphabetical order. Above, Bangalore, India. (Muhammad Mahdi Karim/Wikimedia Commons)

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