On Tue, 25 Aug 2015 07:22:26 -0400, Wayne.B
wrote:

On Mon, 24 Aug 2015 23:54:35 -0400, wrote:

I was never sure why it should cost that much. I guess running RO from
sea water is tougher than brackish well water.
Basically you just need a high pressure pump and a membrane/vessel for
that along with intake and polishing filters.
Since you are not really pumping that much water, I suppose it could
run off the house battery.

===

It takes more pressure as salinity levels go up, much more, something
like 2,000 psi for standard sea water. It takes special membranes to
stand up to that kind of pressure and a lot of power to drive the
pump, typically several horsepower. The pumps will not run very long
from a battery.

The membranes are expensive and require special maintenance routines
to maintain their effectiveness. That involves a lot of extra valves
and plumbing. The better units also have computerized controls to
automate the maintenance routines.

Some guys have tried to homebrew inexpensive systems using pressure
washer pumps but the pumps fail very quickly in a salt water
environment.

OK now I get it. I assumed making fresh from sea water was tougher
than using the brackish water they normally use (like your CC plant
and the Sanibel plant)
I am surprised they don't sell more distillers. It would seem that
waste heat from the engines would be perfect for that. I know that is
where the water came from on the CG ships but it was still pretty much
rationed.
Fresh water at sea is really the most important thing to have.
You can go a long time with just about everything else and food is
swimming all around you.
I never really go anywhere and I still carry a fairly good supply of
bottled water, mostly to give to kayakers (see we did get back on
topic) ;-).