"Pakistan's entire economy is driven by the textile industry," said Michael Kugelman, a South Asia expert at the Woodrow Wilson International Center for Scholars. "The problem with Pakistan's economy is that most of the major industries use a ton of water—textiles, sugar, wheat—and there's a tremendous amount of water that's not only used, but wasted," he added.

The same is true for India.

That impact is an important part of a complex water equation in countries already under strain from booming populations. More people means more demand for water to irrigate crops, cool machinery, and power cities. The Indus River, which begins in Indian-controlled Kashmir and flows through Pakistan on its way to the sea, is Pakistan's primary freshwater source—on which 90