It seems salt is a common topic on those forums: see here and here.
If you wanna create (fresh) water, creating a source seems off because magic can create the material (water), but once. And when the water flows, the source is dry... unless you invest an item with unlimited uses and environnmental trigger (round for example), but then you are bound by the not-ritual effects rule... unless you invest it with the various means to put ritual effect in items... which will still be limited.
So in short, maybe finding a normal source of water and take the salt / other bad substances away (but sincerely, I thought that the medieval paradigme would prevent the concept of "bad water" unless in the form of crawling little demons of sickness swimming in the water... which your favorite ReVi ward against demons or the never waster PeVi Demon's eternal oblivion will take care of ?).