I was wondering if a person could use water breathing to avoid breathing a toxic atmosphere.
The spell itself states:
This spell grants up to ten willing creatures you can see within range the ability to breathe underwater until the spell ends. Affected creatures also retain their normal mode of respiration.
How does water breathing physically affect the target?
For example: When entering a dungeon which was sealed long enough so that there is nothing but CO2, the adventurers figure that out and enchant themselves with the water breathing spell. Could they expect to survive by breathing their full waterskins?
I'm hoping for a strict analysis of the RAW, if possible.
Ultimately this is an edge case for a DM to adjudicate for their table. So I'm going to address the most likely interpretations and the argument for each. RAW, the spell grants "ability to breathe underwater until the spell ends".
A strict interpretation No, breathing your waterskin won't work. You are not "underwater". In the scenario posed above, this will likely keep the characters out of the dungeon. Not fun.
A loose interpretation Yes, the intent of the spell is to allow you to breathe water. Your water skins will work, but only about as long as a bag of air would in a similar situation. I.e.: one extra breath. In the scenario posed above, this will give the characters more time to look around but still keep them out. Still not fun.
A fun interpretation Yes, they can breathe out of the water skins for as long as the spell's duration. It magically grants you the ability to breathe water, and is not concerned about the physics of the question. In the scenario posed above, this will allow the characters to enter the dungeon, and require them to keep one hand occupied with managing the water skin. If they lose it, they must share or they are in mortal danger. This is a creative use of a spell and heightens the difficulty and excitement of the situation, making this particular dungeon delve a unique and memorable experience.
I know which one I'd choose.