Oh, with some further testing, it’s not swamp water that’s causing this problem, it’s being in the swamp that’s causing the issue. If you take water from the swamp, and then leave the swamp with it, it shows up in the crafting screen, but walk back into the swamp area, and suddenly according to the crafting screen, you don’t have that ingredient. As long as you’re in the swamp, you can’t use water for crafting. And I had the same thing near a river too.
Aha, or specifically, if any pool of swamp water (or apparently river water, perhaps other sources) is within the range that you can take crafting supplies from, then it shows you as not having any water/salt water to use in the crafting screen.
