[autarchprinceps]

While I don't doubt there will be rising tensions over access to natural fresh water, I somehow doubt that it would actually be transported, at least on a global scale.

For that the sheer amount you need, the transportation costs, and the already existing, never mind the potential improvements in, desalination solutions are just too disproportionate in costs to each other to actually be at least exactly like oil today. It's more a problem of how expensive is it going to be to have enough drinkable water locally, then that it is ever cheaper to get from somewhere far away. Also depends a lot on the electricity prices and amount thereof we are going to have available.