L20 high elven ranger fighting through water temple. Received following message:

You hit the Snake from Beyond and critically injure it. The water elemental breathes water at you! The Snake from Beyond is hit by the water and annihilated.

I did not take any damage from the water breath attack. I did not receive experience. I have filed this under "feature" because it is a lack of code (monsters can not have intrinsic water-breathing) rather than a malfunctioning piece of existing code.