IN ANCIENT SUMER, the residents of Umma destroyed the water supply of a rival city-state. India and Pakistan have crossed swords over the Indus River. The relationship the United States shares with Mexico owes a fair part of its gritty tension to the overused rivers of our arid border. In James Workman’s Heart of Dryness, all these conflicts and more are merely a taste of what’s to come in a world of population growth and climate change, a prelude to what he calls “an age of permanent drought” that is “coming soon to a landscape near you.”

Workman, who worked in southern Africa as a water expert, gives voice to the true experts in water conservation. They’re not the dam builders, the bureaucrats, or the consultants from international NGOs; rather, they’re the Bushmen, some of whom still manage to make a living in some of the world’s most arid places, facing almost unimaginable extremes of drought and heat and thirst.

And oppression, for Workman’s tale also focuses on the Botswana government’s efforts, launched in 2002 at the onset of a severe drought, to evict the last Bushmen from the heart of the Kalahari Desert by cutting off their water supply. The goal was (accounts vary) to ease access to the desert for tourism and conservation, or to allow large-scale diamond mining, or simply to exercise control because a modern government cannot tolerate a group of people who refuse to submit to its largesse in providing water and other services.

Workman recounts how a tribal elder, Qoroxloo, and her clan stuck out what amounted to a siege through sheer doggedness and a sophisticated knowledge of how to draw the last drops of water from the desert’s plants, animals, and buried wells. Some dodge officials as they hunt and gather; some smuggle water into the desert; some testify in a national courtroom drama that has become about as epic as the long drought.

The book is rich with detail both about how Bushmen live and about the perilous situation much of the rest of the world faces with regard to its future water supplies. Regrettably, Workman’s storytelling never really sings. Too often scenes that must have been vivid in real life — sitting around the fire with a group of Bushmen, or getting stranded in the desert — never quite come to life in the narrative.

But taking the reader to the Kalahari really isn’t Workman’s purpose. It’s showing how the Kalahari is likely coming to us, and soon; it’s outlining what the author calls “the end of dependence on easy access to government provision of abundant freshwater.” It’s introducing an interesting idea about water management — namely, that people might use water much more sensibly if it were provided in small but inalienable individual endowments that could be hoarded, sold, or bartered. But the greatest lesson he draws from the Bushmen is that it’s their intricate social web, more than individual know-how, that allows them to live together in a dry place. If it’s true that “drought splits us apart,” it is also water’s singular power to enforce the bonds between us that may be its most magical quality.