People have been predicting the end of the world since the beginning of the world. So far none of them have been right. There's roughly 332,500,000 cubic MILES of water on the earth. Where, exactly, are you suggesting it's all going to go to?
The earth has enough water to last much longer than that. All the water on earth stays on earth, it's recycled over and over, at least most of it is. The problem is getting the water to places where it's scarce, or moving those people to where the water is.