Saudi Arabia is maintaining its air offensive in Yemen, and Houthi rebels continue to stage assaults. A humanitarian crisis appears imminent.

But another crisis is raging in Yemen that could pose an existential threat to one of the world’s most troubled nations.

Experts predicted in 2010 that Yemen could be the first country to run out of water. Today, half of Yemen’s population–about 13 million people–struggles to secure sufficient supplies of water. Even in Sanaa, the capital, only 40% of households are connected to the municipal water supply. As much as 80% of the conflicts in Yemen’s hinterlands are fought over water—and 4,000 people are killed every year.

I learned of Yemen’s water stress several years ago while researching a book on Pakistan’s water crisis. There are similarities: Both countries are parched, poor, populous, and rapidly urbanizing–all of which can make demand overwhelming. And in both countries, existing resources are poorly managed because of leaky infrastructure and wasteful agricultural water use.

Water shortages are not merely an affliction of the developing world, as California’s recent mandatory restrictions show.

Few countries, however, are as vulnerable as deeply impoverished Yemen. And while fighting for political control will eventually stop, the water crisis will not. Already, water insecurity has been exacerbated by recent unrest that has cut off supplies to some areas. Some locals have been without water for at least five days.

Humanitarian groups are starting to arrive and will provide some much-needed temporary relief. But there may be little they can do to prevent the day when Yemen runs out of water altogether.

The opinions expressed here are solely those of the author. 

This article was originally published in The Wall Street Journal's Washington Wire.