SAN FRANCISCO (MarketWatch)—As the global economy grows, the world is going to get a lot more thirsty in 2030 if steps aren’t taken to cut back on fresh water use now, the United Nations says.

At current usage rates, the world will have 40% less fresh water than it needs in 15 years, according to the United Nations World Water Assessment Program in its 2015 report, which came out ahead of the U.N.’s World Water Day on Sunday.