In the late afternoon of November 5, 1913, a crowd of ﬂag-waving Angelenos gathered to watch the christening of the Los Angeles Aqueduct, a network of canals, pipes and tunnels that would quench the thirst of their parched and growing city. The chief engineer of the aqueduct—a mustachioed man named William Mulholland—stood in the glaring California sun and gave a historic address. “This rude platform is an altar,” he began, “and on it we are here consecrating this water supply and dedicating the Aqueduct to you and your children and your children’s children—for all time.” Then, he leaned over the railing and gestured to the wall of water cascading down the concrete culvert. “There it is,” he said. “Take it.”
The crystalline waters before him had traveled some 230 miles from the eastern slopes of the Sierra Nevada mountains. Built over the previous ﬁ ve years, the aqueduct would carry 260 million gallons of water a day from the Owens River across the Mojave Desert and through the San Gabriel Mountains, where it entered the city’s water system.
Today, the city draws more water from outside its natural watershed than any other in the world. To safeguard its water, Los Angeles owns about 315,000 acres in the Sierra watershed, yet with warmer temperatures, more frequent forest ﬁ res and decreased snowfall, the supply is in jeopardy. The region is in a state of “water stress”: It uses more than 40 percent of the water available to it.
Los Angeles represents an extreme case of how fresh water forms a bond between the concrete jungle and the natural world. When we turn taps on, we take for granted that clean water will ﬂow out. But accomplishing this feat takes a lot of infrastructure: Cities move about 130 billion gallons of water per day a distance of nearly 17,000 miles. About 41 percent of Earth’s land area acts as a funnel for urban regions, gathering rainfall and directing it toward the 3.9 billion people who live in cities. These lifelines will be under intense pressure. The United Nations Population Division predicts that the world’s urban population will expand by 2.5 billion by 2050. Much of this growth will occur in cash-starved developing countries in Africa and Asia that can’t just build their way out of scarcity, as Los Angeles did.