Four Million People Across the World Lack Drinking Water at Some Point in the Year

A new approach to quantifying the global water-scarcity crisis shows that the degree to which many regions across the world lack sufficient available water to drink, bathe or irrigate their crops is far more significant than ever imagined.

Scientists typically measure water scarcity on an annual basis. In that accounting, half a billion people in the world face severe water scarcity all year round. But new research published Friday in Science Advances used a monthly analysis, and found that 4 billion people live under conditions of severe water scarcity for at least one month out of the year. Nearly half of those people live in India and China.

To determine water scarcity, the team "established the maximum sustainable 'water footprint' for every location on earth, and then looked at actual water consumption," says lead author Arjen Hoekstra, a professor of water management at New Zealand's University of Twente. "If the latter is much greater than what is sustainable, then there can be said to be severe water scarcity."

Hoekstra says the findings show that water scarcity is deserving of its place alongside climate change and terrorism among the World Economic Forum's top three global problems. Of the 4 billion people affected by water scarcity, those in Mexico, the western U.S., northern and southern Africa, southern Europe, the Middle East, India, China and Australia regularly experience water shortages that make it difficult to sustain households, industries and farms. In other areas, water supplies are still fine but at risk in the long-term.

The study also found that people live under different levels of water scarcity, from low to severe. Sixty-six percent of people experience "severe" water scarcity at least one month per year, but 71 percent experience " moderate to severe" water scarcity at least one month. The number of people facing severe water scarcity for at least four months per year is estimated to be between 1.8 and 2.9 billion.