[spenrose]

This perspective dates to at least 1940, when the population was a fraction of the current size. The fantastic Charles C. Mann wrote an excellent book, The Wizard and the Prophet, about it.

Regarding water specifically, we now have multiple desalination projects of 1MM m^3/day, enough to support a city of 4MM people. They are expensive, but getting cheaper, and real (rich) polities in the Middle East are relying on them.