Kayerloth wrote:You'll notice that there aren't any record of any pre tech societies who've managed that. the major problem is that while desalination sounds nice, it's extremely engineering intensive to get it to scale beyond beaker stage.
No need for magic.
There are a large variety of desalinization processes that could be used. I'm no expert (or engineer) but one of the simplest methods is likely via solar 'power'. Basically evaporate the water off (from your salt water supply - something the sun does naturally), then condense and collect the water. The hard part according to the Wikipedia article I read is probably getting the solar energy concentrated on a small area to cause the natural process to speed up sufficiently for any large scale use.
Short read: Look into Desalinization on the Web.
Good point, though the knowledge is also probably lacking in those pre-tech societies and probably also be lacking in most imagined medieval fantasy settings so there is that as well.
Maybe instead a Permanent Wall of Fire (heat source) plus tubing and make a distillery.
Or just go back and use teams of 'create water' or 'create food and water'. Water from the later appears permanent (doesn't vanish after 24 hours).