People have used groundwater for thousands of years, especially in arid regions such as the Middle East and North Africa, where hand-dug wells and subsurface tunnel systems collected and diverted it for early societies. These ancient methods amounted to skimming the shallow groundwater off the top of massive aquifer systems—the vast stores of invisible groundwater beneath the continents that account for more than 95 percent of all circulating fresh water on Earth.
Throughout history as cities grew, new water infrastructure was built to supply this vital resource to increasing numbers of people. Initially, urban dwellers carried water from hand-dug wells and lakes and streams that ran through the city. As cities advanced, engineers built aqueducts and canals to import water from great distances. Among the engineering marvels of the ancient world, the Roman water system of elevated aqueducts, underground piping, and the world’s first sewer network is an iconic example of the ingenuity that made possible Europe’s first city of a million people.
In March 2018, torrential rains poured over the Australian Outback in the state of Queensland. The water pooled and began dispersing into rivulets for a long march to the Lake Eyre basin, which bottoms out 50 feet below sea level—the lowest point in the country. Over the course of weeks, the runoff filled innumerable channels that in turn fed into three river basins—the Georgina, Diamantina, and Cooper Creek—and advanced toward Lake Eyre like one massive aquatic organism, transforming a sweltering and inhospitable landscape into one alive with plants, wildlife, and birdsong.
In the spring of 2018, Cape Town, South Africa, narrowly escaped shutting off drinking water taps for its 4 million residents. Three consecutive years of drought had dried up its reservoirs. City officials began publicly announcing “Day Zero”—the date water would no longer flow to household faucets. At that point, residents would need to retrieve their rations of drinking water from one of 200 distribution stations around the metropolis.