Writer and National Geographic Fellow Paul Salopek’s Out of Eden Walk is a decade-long storytelling odyssey across the world. He is walking in the pathways of the first human migration out of Africa to the tip of South America. This is his latest dispatch from India.

“Do you do magic tricks?”

It is the villagers. They watch us pass under the blinding white sun of the Thar Desert. We are walking across India with a cargo donkey. Local people mistake us for vagabond performers, traveling quacks, circus nomads. The answer to their question of course is: yes. We carry magic. But so does everyone.

It lies in water.

Human beings are mobile wells of mildly salty water. As every schoolchild knows, our bodies contain the same fraction of water—71 percent—as the portion of the Earth’s surface that is covered by oceans. This is no mystery. We are water animals born into a water planet. Water is everywhere and nowhere. It is a restless compound—transitional, unstill, always on the move. It shape-shifts constantly from gas to liquid to solid and back again. (Even frozen at the South Pole into a mile-and-a-half deep cap of ice that is one million years old, it still flows, albeit slowly.) The oceans hold 97.25 percent of all the water on the globe. The poles and glaciers trap 2 percent. The absurdly small, drinkable droplet that remains— the precious 0.75 percent of liquid fresh water that Homo sapiens relies on for survival—we squander like madmen raving in a desert.

In India, a country of 1.3 billion people, fully half the population lives in a water crisis. More than 20 cities—Delhi, Bangalore, and Hyderabad among them—will gulp their entire aquifers dry within the next two years. This translates into a hundred million people living with zero groundwater. Farmers in the Punjab, one of India’s core breadbaskets, complain that their water tables have dropped by 40, 60, or 100 feet in a single generation. A water inheritance amassed since the last Ice Age, across thousands of years, is being pumped out tirelessly by industrial agriculture, by the Green Revolution. The government’s response? Build more large dams (India has 5,000 already) and re-channel the course of rivers to quench the thirst of parched regions. Meanwhile, the vital monsoon rains grow more erratic with changing climate. And demand for fresh water swells by 16 million new human beings a year.

“Conservation? Nobody talks about it,” says my walking partner Arati Kumar-Rao, a nature photographer who has lived among the dry-land farmers of the Thar.

View Images Centuries-old wells like this one dot the Thar Desert of Rajasthan. Photography by Paul Salopek

The rain harvesting technology of India’s desert dwellers is ancient and complex. They look carefully at the broad roll of the land, noting gentle depressions called aagor—sky catchments. They channel the scarce rains down these barely perceptible slopes to ephemeral ponds called khadeen. These rain-fed reservoirs they have farmed for centuries, perhaps millennia, without irrigation, growing drought-resistant crops like millet.

Kumar-Rao and I pause at desert well. The sun is toxic. It is 113 degrees Fahrenheit. We are thirsty. I drop a tin bucket through a trapdoor. I hear a splash. I yank up delicious weight on a rope.

“Hah!” a man shouts. “What are you doing?”

He has appeared from a hut. He is a shepherd. This is his rainwater, collected radially, from many sun-cracked acres around, into this hand-dug hole. You can drink what you wish he tells us—this is every traveler’s right—but you cannot wash.

Video by Paul Salopek

When we finally part ways, Kumar-Rao and I, in the pilgrimage town of Salasar, she will soak her sore feet in a bucket of transparent liquid.

The comfort of water on water.

* * *

One oxygen atom. Two atoms of hydrogen.

Water molecules are bent like an arrow tip, like an elbow. This gives them a certain polarity, an infinitesimal charge, that collectively shapes the world. They are the magical solvent, binding and dissolving brain cells, mountains, the steam of morning coffee, tectonic plates.

I walk the edge of the Thar Desert.

I pass through villages where changing water use is silently poisoning people. In the past, surface rainwater alone was enough to meet the demands of humanity. Now, modern agriculture and population growth have pocked the land with thousands of bore wells: machine-drilled capillaries whose pumps tap deeply into groundwater. But not all of this once inaccessible supply is healthy. It contains minerals. Fluoride. Arsenic. It varies from place to place. This is half of the crisis—not quantity, but quality.

“Do you know your fluoride level is above safe standards?” my new walking partner, the environmentalist Siddharth Agarwal, asks gathered villagers.

View Images Siddharth Agarwal measures the fluoride level of water from village wells in the Thar Desert. Photography by Paul Salopek

Agarwal, who has trekked thousands of miles along rivers in India, often stops to test the water of village faucets along our route. He uses a device attached to his smart phone that measures fluoride levels. A few drops of water go into a canister. He snaps a photo. The color of the water, analyzed by an app, reveals its mineral content. Excess fluoride causes teeth and bone disfigurement.

The villagers nod somberly. They often know about fluoride. But what can they do? The authorities have promised a filter. While they wait—some have waited years—they buy water delivered by tanker truck. Or they drink the slow poison. Our bodies are living wells. One cannot go without water.

“The most important surface isn’t the one we’re walking on,” Agarwal tells me. “It’s the water layer below our feet.”

He views landscape through this X-ray prism. The trees change, the crops change, human life changes, all depending on the wet topography below. A vanishing liquid underworld.

Weeks later, crossing the brackish Sambhar Lake basin near the city of Jaipur, I watch women at work. They earn three dollars a day. They walk blindly backwards for hour after hour, raking up salt across a vast plain of scorching white. Heat-bent light swallows their legs, delivers them back. An infernal vision. Some sorcerer’s bitter abracadabra. But it isn’t. It is us.

View Images A salt worker toils near the ancient city of Jaipur, in Rajasthan. Photography by Paul Salopek

This story was originally published on the National Geographic Society’s website devoted to the Out of Eden Walk project. Explore the site here.

Paul Salopek won two Pulitzer Prizes for his journalism while a foreign correspondent with the Chicago Tribune. Follow him on Twitter @paulsalopek