Desalinators are used to produce freshwater out of saltwater, with the salt being a byproduct.
I reuse my salt water by recycling the reef water from my 210g into my 120g fowlr/softie tank. Just recycled 140 gallons last week. I figure the 120g with 90g seahorse refugium/sump has the dirtiest water so that is siphoned down the drain & the reef water is much cleaner so the 120g system now has better water in it, even though it is not new water.
I have joked with TomR for years that I wanted him to save his change water so I could recycle it in my tanks, but now I do it in-house
Been recycling the sw for over a year now, with no negative effects on my 120g system. I even have a Yellow Magnifica & a couple of Rose BTAs in the 120g & these anemones are doing great (the RBTAs even cloned).
Anthony