You have to complete holy water part 2 now. So press
H to get to the help guide and click on the Quest tab. You'll see a few lines, some with 0's and some without. click the arrow to expand the menu and find the quest info your are working on. Click that line and the info will appear on the right side.
So, doing that, you will notice that you must complete Holy Water 2, to finish that series of quests. You'll need to talk to the Clergy at the Sophia Cathedral. Once you get the holy waters go back to the stable and stand near the building and right click them in your inventory until you end up with 5 stable filths.
Good luck
