I have been focused on Peak Oil, however that is not the only resource that we need, and is even less essential than some, particularly water. And there is only so much water to go around that is drinkable.
On a broad scale this Washington Post article addresses the issues of shortages. We have an increasing population, and a mobile one. That puts stress on the resources in any given location and has created a lot of notions about solving the problem. What if the worst happens, as in Las Vegas? Also, remember that the Hoover Dam does more than provide Las Vegas' primary source of water, it also provides electricity. What happens if Lake Mead's water levels drop to a level that cannot support operation of the turbines? Care to draw that picture? Especially in LA?
The way we use water now determines what will be available in the future. Having enough water is more important than having enough oil. What are we willing to do to ensure a drinkable supply?