Many have worried about "peak oil", but maybe we should have worried about another resource--40 years ago.
For oil, using it involves a chemical transformation that won't be reversed except on geological time scales. Using water often leaves it in its native state, with a cycle that returns it to the environment in a geologic blink of an eye. Still, the authors make a compelling argument that, not only can there be a peak water, but the US passed this point around 1970, apparently without anyone noticing.
Some warn that resource wars are in our future. We've had them in the past; I wouldn't find it unbelievable if we did again.