Anyone near any body of salt water should consider purchasing something like the Navy/Coast Guard [approved] Manual Reverse Osmosis Desalinator (MROD) They are sold on eBay and as far as I know are only made by PUR . They can provide drinkable water at sea for one to two people with quite a bit of work but PUR also makes a larger bicycle pump model. I have tested mine in both
the Med (not as salty as ocean) and the Salt Sea (the saltiest water in the world). More salt just means more work.
A creative person might make a desalinator from a home reverse osmosis filter system but I would highly suggest having at least one PUR hand unit as a backup. The U.S. Navy/Coast Guard issue MROD-06-LS includes a great add-on thigh strap and lever extensions not on the civilian models. – David in Israel