On the Polar Sea we had 2 evaps that turned salt water into fresh water. The system was designed so that you could suck raw sewage into it and have clean, safe water. It used steam from the boilers to heat the water in a vacuum, water in a vacuum boils at around 112 degrees. Uses less energy than boiling in atmosphere. The steam that came off the boiling water ran through a condenser where it was cooled and then into a pair of 10,000 gallon holding tanks. Worked great. The reverse osmosis system was constantly requiring maintenance, filter changes, and cleaning. The evap required no real maintenance, just check the pressure and temps periodically.
If you could build an evap you could store large quantities of water in holding tanks, then you wouldn't have to run your boiler all the time.
The evaps on the Polar Sea produced around 300 gallons of water per hour each. Real efficient machines. The boilers that powered them (and heated the living spaces) burned around 75 gallons per hour diesel. We had two of those as well, but could run both evaps off of one boiler.