The American West set the model, and around the world it soon became a mark of progress when a nation would turn to large-scale management of its water resources. Egypt is one of the best examples. The building of the Aswan High Dam in the 1960s created the third-largest reservoir in the world, tamed the disastrous annual flooding of the Nile, and provided controlled irrigation for more than a million acres of arid land. Built a few miles upriver from the original Aswan Dam (built by the British between 1898 and 1902), the Aswan High Dam was a gargantuan project involving its share of engineering challenges as well as the relocation of thousands of people and some of Egypt's most famous ancient monuments. Spanning nearly two miles, the dam increased Egypt's cultivable land by 30 percent and raised the water table for the Sahara Desert as far away as Algeria.

Egypt solved many of its water-related problems with this one grand stroke, but most countries in the developing world don't have the economic resources for such an undertaking. And in many cases, they don't have the water to work with in the first place. In such cases, one solution being adopted more and more widely is desalination—the treatment of seawater to make it drinkable. Once a pipe dream, desalination is now a viable process, and more than 7,500 desalination plants are in operation around the world, the vast majority of them in the desert countries of the Middle East.

Two main processes are used to desalinate seawater. One, called reverse osmosis, involves forcing the water through permeable membranes made of special plastics that let pure water through but filter out salts and any other minerals or contaminants. The other method is distillation, in which the water is heated until it evaporates, then condensed, a process that separates out any dissolved minerals. Although these and other desalination techniques do work and have solved water shortage problems, they are too costly for many countries; distillation, for example, requires a good deal of energy input, and fuel costs can be prohibitively high. In some cases, adequate supplies of fuel aren't even available, at any cost.

The challenge this represents is a mighty one. For a shockingly high proportion of the world's population, clean water is still the rarest of commodities. By some estimates, more than two billion people on the planet have inadequate supplies of safe drinking water. Most of them still get their water from sources outside their homes-water that is for the most part untreated and rife with disease—carrying organisms. In the developing world, more than 400 children die every hour from those old, deadly scourges—cholera, typhoid, and dysentery. In short, the lack of safe water is a global crisis with a lethal toll.