[mcv]

With access to cheap energy it becomes a lot easier. You could just boil it and collect the condensation.

[pixl97]

That's still pretty damn expensive. Ever leave a pot on the stove boiling and let it run out, the amount of precipitate is surprising. Do that on millions of gallons of water and you end up with a lot of material that needs cleaned often and isn't easy to get off.

[jpindar]

The precipitate from evaporating (or boiling) ocean water is valuable. Take a look at an aerial photo of the southern end of the SF bay sometime.