Do a search on this site for:
Reverse Osmosis Watermaker
Anyway, FYI reverse osmosis
requires a rather expensive machine which pushes saltwater at high pressure through a membrane to remove salt
and yield fresh water. These machines are in the order of US $4000. for a 20gph device (plus installation).
Water filters remove impurities from water that is already fresh. They won't remove salt. However, they can render water safe and healthy for a modest amount of money
. You can probably pop down to Home Depot and have a look at what they carry to get an idea of what the systems look like (marinized systems will do the same thing but will cost more!!).
Welcome to the forum and good luck on your adventure!