Now for the million-dollar questions: Why has so much of modern water management gone awry? Why is it that ever greater amounts of money and ever more sophisticated engineering have not solved the world's water problems? Why, in so many places on this planet, are rivers drying up, lakes shrinking, and water tables falling?

The answer, in part, is simple: We have been trying to meet insatiable demands by continuously expanding a finite water supply. In the long run, of course, that is a losing proposition: It is impossible to expand a finite supply indefinitely, and in many parts of the world the "long run" has arrived.