Economist: “Water is the oil of the 21st century,” declares Andrew Liveris, the chief executive of Dow, a chemical company. Like oil, water is a critical lubricant of the global economy. And as with oil, supplies of water — at least, the clean, easily accessible sort — are coming under enormous strain because of the growing global population and an emerging middle-class in Asia that hankers for the water-intensive life enjoyed by people in the West. Oil prices have fallen from their …