By Chris Arsenault, originally posted on July 25, 2016

RIO DE JANEIRO (Thomson Reuters Foundation) – Contamination as people and agriculture crowd around water sources has hiked the cost of water treatment by 50 percent in some major cities, a study said on Monday, making it harder to provide safe drinking water for a growing urban population.

An expansion of agriculture in areas where cities get their water and growing numbers of people living around watersheds are largely responsible for the rising cost of water treatment, said the study by scientists at Yale University and other U.S.-based institutions.

Nearly 90 percent of the world’s urban watersheds face some level of degradation from agricultural chemicals and increased sediment, making water treatment more expensive, the study said.

The world’s urban population is expected to swell by 2.5 billion people by 2050, according to U.N. data. Providing affordable drinking water to this growing population will be a challenge for governments, especially in fast-growing cities across the developing world.

“We need to manage our water resources more carefully,” Rob McDonald, one of the study’s authors told the Thomson Reuters Foundation.

“When someone upstream decides to expand agriculture or build more houses it will have a cost (on water treatment) which is not accounted for in the market place,” said McDonald, lead scientist at The Nature Conservatory, an environmental group.

One in four of the 309 cities studied has made investments to protect their watersheds such as helping farmers to reduce erosion or properly treating human waste, said McDonald.

Cities such as Tokyo, Japan’s capital, and Boston in the northeastern United States have instituted robust land-use rules for protecting their watersheds, he said.

Others such as St Louis in the central United States and Argentina’s capital Buenos Aires, which draw their water from rivers affected by agriculture, face higher water treatment costs, he said.

“City leaders can use our findings to advocate for protecting their drinking water from contamination, rather than spending billions of dollars to clean it up,” McDonald said.

The study is the first to analyze the economic cost of human activities on water treatment prices in cities, he said.

(Reporting By Chris Arsenault by Ros Russell; please add:; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women’s rights, trafficking and climate change. Visit news.trust.org)