Almost 4 billion people—two-thirds of the world’s population—face severe water scarcity at least one month a year, according to new analysis.

That is far worse than previous estimates of 2 billion to 3 billion people. About 500 million struggle with this acute water shortage all year long.

Earlier estimates focused on assessing year-round water supply. That did not account for fluctuating supplies during wet and dry months and the severe water shortages that typically occur during specific times of the year, say researchers at the University of Twente in the Netherlands.

The affected population lives not just in vulnerable developing countries in Asia and Africa but also in Australia, the United Kingdom, and the American West. And water shortages will get worse.

“Water scarcity will increase because of growing populations and increasing water demand per person,” said Arjen Hoekstra, lead researcher and a professor of water management at the University of Twente.

(Graphic: Science Advances)

Cutting short showering time or letting lawns go dry won’t be enough. Hoekstra said eating habits play a big role in sucking up water sources. But he was pointing the finger at meat, not produce like almonds, which have taken a beating for being a thirsty crop.

“About one-third of the world water consumption is for producing animal products. Their water footprint is larger than that of crop products with equivalent nutritional value,” Hoekstra said.

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“For example, the average water footprint per calorie for beef is 20 times larger than for cereals and starchy roots,” he said. “The meat consumption per person in the world is still increasing, so the water demand grows quickly because of that.”

As temperatures rise because of climate change, dry places are getting drier. And burgeoning demand and more intense and longer droughts are depleting groundwater reserves.

Hoekstra said 500 million people live in such regions, where water consumption is double available supplies. Vulnerable populations include 180 million people in India, 73 million in Pakistan, 27 million in Egypt, 20 million in Mexico, 20 million in Saudi Arabia, and 18 million in Yemen.

Water scarcity is particularly acute in politically volatile regions. For instance, Yemen’s entire population is affected by shortages, while 80 percent of Libya’s and Somalia’s people face water scarcity.