The Ancient Mariner complained abut the lack of drinking water on his ship in 1798 but fails to mention (perhaps Coleridge didn’t know) that Samuel Pepys had requested one of his naval captains to carry out “… an Experiment of producing fresh water (at Sea) out of Salt” as early as 1684. The outcome of that is not known, but it can’t have been that successful as onboard desalination doesn’t seem to have progressed much until the invention of the multi-stage flash (MSV) distillation process in 1955.