Unlikely a problem given the discovery of a largest fresh water bodies ever known was just discovered: http://inhabitat.com/scientists-discover-freshwater-reserves...
Granted, though, if 100 centuries' worth of water is really extractable, this may be pushing the problem so far into the future that we can buy a lot of timer for better solutions.
I think many knee jerk liberals haven't yet internalized this viewpoint, and don't (yet) have great answers to that question. (Or turn it around: if you think this is wrong, but don't have a good answer, that makes you a knee jerk liberal!)
PS: I say this as a centrist liberal.