That's quite an easy way to run out of water.

Water doesn't vanish after it's used. Also, putting your first number in scientific notation helps put this in perspective: 2.2 x 10^12 . Seven orders of magnitude. Close to 15 000 0000 times as much.

That's not to say that work isn't needed to develop cheap recycling appliances, and to build water systems that recycle and reuse waste water rather than dumping it all into the environment, but it's not a very hard problem on the scale of things humanity can accomplish -- it mostly just requires more energy.

Energy will continue to be the limiting factor for a long time, and eventually (after essentially perfect recycling of all material civilization requires) the limit will be waste heat. But as others have mentioned, we have a whole solar system to use as well, and moving the highest heat processes to space would allow us to radiate it away without affecting the earth. Technology which is clearly within our reach would allow the earth to support trillions of humans -- admittedly at a more crowded level than I would prefer. :)