On Fri, 21 Sep 2007 17:35:02 -0500, Brian Whatcott
wrote:

The boiling point of water at the top of a sealed 40 ft column of
water is near ambient.
So, it doesn't take much heat to boil the brackish water, and have it
pass to the fresh column where it is slightly cooled to hold the near
vacuum conditions at the boiling level.

Fraid not. It takes the same ammount of heat to boil water as at 212F.
Approximately 1175 BTU/lb. You might save a little not heating the
water all the wqy to 212.