The first, and biggest, of the world's water problems is that the available water is not naturally distributed, in space or time, the way we would like it to be.

In the beginning, people settled by rivers, lakes, or springs because that was the only way to have access to water supplies without which they could not survive. Then we learned to move water around, sometimes over remarkable distances, in aqueducts and pipelines. Agriculture could not develop in arid lands until we learned to build and maintain often-long canal systems. So we started to deal with the initial unsatisfactory geographic distribution; human settlements spread, and irrigated lands stretched to the horizon.

But there was also a problem with distribution in time. In many places rainfall (or show) came in the winter, but the maximum need for water was in the hot, dry, summer. So we learned to build dams and store water, so that the winter rainfall, or snow-pack, could be used when it was more needed - in the summer.

As we start into the Twenty First century the biggest less-than-fully-developed rivers are like the Amazon and the Congo, located far from big cities, and in humid areas where agriculture is possible without irrigation. Most of the world's major feasible dams have been built, and the cost of re-arranging Nature is now becoming prohibitive.