Anyone know of some estimates of the (energy) cost of desalinating seawater, vs. shipping in freshwater from where it is plentiful? (as a function of distance).

Anyone know of some estimates of the (energy) cost of desalinating seawater, vs. shipping in freshwater from where it is plentiful? (as a function of distance). Doesn't seem too far fetched that in near future, eg. oil tanker ships could be re-purposed for that job.