Wetwork.
*snerk!* Good one!
Thanks for all your suggestions, guys! I ended up having the group being tasked to go to an isolated temple of Istishia, once a retreat, but abandoned due to some crises elsewhere. Nearly simultaneously, the pure waters of the temple had gone sour. The group had to travel to the temple, figure out why the springs had gone bad, clear them and get them flowing again, as well as clearing out things that had moved in in the interim.
If they end up needing a favor in the future of Istishia's temple, I'll definitely keep some of these others in mind!