That question can't be answered in static terms.
The world will never run out of water because water doesn't leave the world. But the world's water cycle only produces so much drinkable water each year. If our use rises beyond what's available, we're in trouble.
Now, once again, that's unlikely to ever happen on a global scale, but local effects happen all over the place. It's entirely possible for a region's water use to outstrip it's water supply, by relying on wells and lakes. Once those sources run dry, you've got a population center and no way to get them the water they need.
On an individual level, you can always go somewhere else. Entire cities picking up and moving is less plausible. We can't dehydrate the whole world, but we can definitely make it less habitable for future generations.
