I under stand that the lower the air pressure, the lower the boiling point of water. Also, some primitive desalination kits are basically evaporators.

Could you make a really big tank without a bottom and paint it black. Then, submerge it partly in the ocean . Pump the air out of the top. The water would rise up into the tank, a bit, but not all the way.

You wouldn’t need to have a perfect vacuum, just lower the air pressure enough to make boiling easier. Let the sun heat the black tank, and viola, steam.

Collect that steam from the air you are pumping out of the top of your tank, and you’ve got fresh water, right?

Edit: nevermind. Found it on google. Leaving this here to display my shame.