I'm starting a new 5e campaign with my players where they are all demigod, inspired by this blue text https://imgur.com/gallery/7zzpt
They are still figuring who they want to be and what God they want to be a demigod of. In the story, the demigod are immortal, and don't require food, water, or air. The subject of drowning came up because one player wants to control water, and in case he were to betray the party, they wanted to know if they would be safe or not.
The writer in the story does mention their god stops them from breathing, which he said wouldn't kill him, just would feel bad. I'm just not sure if drowning would be different.
Is there anything RAW or canon that says immortals or gods can't drown, or that beings that don't require air wouldn't drown?
Edit: if not 5e, do the other editions have this information. I thought I had seen books specifically about deities.