With the growing population our attention will be divided between providing enough food, battling and curing diseases etc. All of these require water. Human activities are preventing us from even preserving the little water that we have now. We also don't have the energy to actually use the water from our oceans. So before anybody can actually try and make water appear out of thin air, we might all be dead.
In the future, we humans may devise a way that may allow us to make water appear out of thin air. Sure, that sounds unrealistic right now, but in the future, some bright mind may develop a method to solve the problem of humans running out of water to drink and use for any other purpose.