By 2040, most of the world won’t have enough water to meet demand year-round

Seven out of 10 people on earth can count on running water to be available in their homes. That means it’s always there when we need it, whatever we need it for.

Until it isn’t: Cape Town, London, Sao Paulo, Jakarta, Istanbul, Tokyo, and Mexico City could be facing “Day Zero” — meaning they will run out of water — in the next few decades unless their water use radically changes.

Less than 1 percent of the world’s water supply is readily available for human use (the rest is salty, frozen at the poles, or trapped underground). Yet we use it in wildly inefficient ways: We lose it to leaky pipes. We dump waste in it. We try to grow some of our most water-intensive crops in the desert. Really.

So how have we built a world where we don’t have enough of its most valuable resource? What happens when we run out? And what can we do to solve the problem now?

Vox tackled these questions on this week’s episode of our Netflix show, Explained. We have new episodes every Wednesday on topics ranging from gene editing to dieting to the racial wealth gap and more. If you like our videos, then you’ll love this show; it’s our most ambitious video project to date.

To watch, search “Explained” on Netflix or go to Netflix.com/explained. Click the “My List” button to make sure you don’t miss an episode.

Cape Town is bracing for “Day Zero” — the day it cuts off running water for 4 million people (Zeeshan Aleem, Vox)

America has a water crisis no one is talking about (Sarah Frostenson, Vox)

The Flint water crisis, explained (Libby Nelson, Vox)

Cape Town Averts ‘Day Zero’ By Limiting Water Use (Ari Shapiro, NPR)

Is Water The Petroleum of the Next Century? (A video by the Wall Street Journal)

Mexico City, Parched and Sinking, Faces a Water Crisis (A New York Times piece featuring Arnoldo Matus Kramer, Mexico City chief resilience officer, whom we interviewed for this episode)

As Big Beer Moves In, Activists in Mexicali Fight To Keep Their Water (An NPR report about Mexicali Resiste water activists taking on a new brewery to preserve their water supply. We interviewed Mexicali Resiste activist León Fierro Reséndiz as well as local farmers Alvador and Laura Mena García for this episode.)

Mapping Drought And Water Stress, From Arizona To Zimbabwe (WBUR interviews Betsy Otto, a water resource analyst whom we also interviewed for this episode)

Researchers Link Syrian Conflict to a Drought Made Worse by Climate Change (Henry Fountain, the New York Times)

The Water Crises Aren’t Coming — They’re Here (Alec Wilkinson, Esquire)

Fragile countries risk being ‘stuck in a cycle of conflict and climate disaster,’ Security Council told (A UN News brief about food and water scarcity featuring Deputy Secretary-General Amina Mohammed, whom we also interviewed for this episode)