For most of history, thirsty humans made do with what moisture fell from above: The sun warmed the salty seas, pure water evaporated into the air and then cooled and fell to the earth as precipitation. There it clung to glaciers, froze and thawed in lakes, was absorbed by plant roots, coursed through fractured bedrock, and seeped slowly through soil, into aquifers. Most of it returned to sea and sky all over again. There is as much of that water on the planet today as when the first amphibian flopped ashore; as much as when the ancient Greeks divined the future in the babble of brooks.
So why do experts in science, economics, and development warn that a "global water crisis" threatens the stability of nations and the health of billions?
From space, the idea of a global water crisis may seem perplexing: 75 percent of the planet's surface is blue. But usable fresh water is a tiny fraction of what we see – only 2.5 percent of the water on Earth. And two-thirds of that fresh water is locked away in glaciers, icecaps, and permanent snow. Of the stock of accessible fresh water, 99 percent is in underground aquifers – some are nonrenewable; and in some that are replenishable, ground water is slurped up faster by a growing population than it can be replaced.
But even so, say experts, the problem is perhaps more an issue of recognizing water's true value, using it efficiently and planning for the lean times, than it is a lack of overall supply.
The ongoing historic American drought, with its cascade effect on food and utility prices at home and food costs abroad, is an example of scarcity's effect.