Cheeseroo, it comes down to cost... Desalination plats are ridiculously expensive, both to build as well as operate... Especially the ones that operate off of electrolysis, the amount of electricity used is CRAZY... Towards the end of my time in the Navy the submarine i was stationed on had a reverse osmosis system installed as a solution to the desalination issue for fresh water generation.. Prior to that they had a boiler system.