I am trying to get past the elven ritual in the Brecilian ruins (filling the earthen jug with water, placing it on the alter, praying, sipping, and pouring the water back into the fountain), but I keep running into a problem.
Whenever my character puts the full earthen jug onto the alter and prays, it boils away. What am I doing wrong here? I’m doing my best to follow the instructions from GameFAQs, but they don’t discuss this annoying boiling contingency.

You’re supposed to have the codex entry before you’re able to do the ritual.