Which will happen first?

1. Our societies will learn to curb our use of water
2. Our technologists will discover/invent a way to purify and transport water effectively to keep up with our rising demand
3. We will perfect the art of splicing genes and adapt our species to be able to consume salt water directly
4. We will hit the water cap and see our species growth top out and/or start shrinking
5. Water will not be the limiting factor because we will have already have experienced extinction or massive population reduction due to some other limited resource and/or foolish action

I would be hard pressed to ever make a bet on humanity curbing consumption.

Run technologists, the clock is ticking.