Good news, I was able to refill my water skeins using an underground spring down here.
(Bad news: it tried to wash me off my feet into a lava lake. Good news: I didn’t let it. Tying one’s to a secure stalactite is always a good idea when exploring unusual places.)
So I don’t have any burn cream but I do have all the appears-fresh-and-clean flowing water I want. And that’s a good thing any day of the week.