The Wizard and the Prophet: Two Remarkable Scientists and Their Dueling Visions to Shape Tomorrow's World

by Charles C. Mann

What isn’t in doubt is that water—H2O—is one of the most common molecules on Earth, perhaps the most common. Which makes the idea of water scarcity seem odd. How could people run short of something so abundant? The reason is that 97.5 percent of the world’s water is saltwater—undrinkable, corrosive, even toxic. More than two-thirds of the remainder is locked into polar ice caps and glaciers, the great majority of it in Antarctica. The rest—all of the planet’s lakes, rivers, swamps, and groundwater—is less than 1 percent of the total. That is the theoretically available freshwater supply. Put together, it would form a sphere about 170 miles in diameter. In fact, though, this is a wild overestimate, because more than nine-tenths of that water is groundwater, and most groundwater is unusable or inaccessible. Although water is common, the total global supply (large sphere) is less than one might imagine. Smaller still is the total supply of freshwater (medium sphere), and most of that is locked up in glacial ice or buried too far underground to reach. The total supply of available, usable freshwater—all the water for the world of 10 billion—is shown in the tiny sphere. Credit 46