I certainly agree that water is a precious resource and shouldn't be wasted, not because of lack of supply but because it's simply the prudent thing to do. However, the earth is 1/3 land mass & 2/3 water which means the real shortage now and in the future will be in Land/Real Estate.
We have too much Water & Not enough Sand.
The Water issue has been resolved for many years via "Desalination" which is already in use throughout the world. So I guess if we deplete the vast oceans of H2O, Mars here we come!
We should be more focused on the real pending issue which is pollination and related subjects. Pesticides and other contaminants are "taking out" the bees.
Bottom Line - You'll probably drop from lack of sustenance because you can't get a ham sandwich about 1000 years before you dehydrate from lack of water. At least that's the case here in the U.S. and most other countries around the world.
P.S. If it wasn't for political roadblocks we would have "Desal Facilities" along the shores of Africa married to pipeline delivery systems servicing those who are in desperate need.