If water is required to survive and there is a limited availability of it from conventional sources, desalinization will be used on a large scale to make up the difference regardless of cost. The point is that the technology already exists and is supplying 70% of the drinking water to more than 25 million people in Saudi Arabia, a place I lived for five years. ///////////// All true.
But people don't just want to survive, they want to prosper. The way to prosperity for some and to ensure prosperity for others is to collapse the cost of currently relatively expensive water desalination.
That's just what's happening now with photo voltaics. Either the demand for energy could get so high that photovoltaics at current prices would make sense for large scale adaption--or the cost of photovoltaics could come down so as to be competitive with coal.
What's happening right now is that the cost of photovoltaics is coming down so as to be cost competitive with coal. Some huge fab plants in silicon valley are coming onstream this fall using semiconductor production techniques and minimal silicon that will reduce the cost of photovoltaic cells to 1/5 current costs this year and 1/10th current costs in the next 3-4 years.
You can read about it
herein the context of a post on desalination.