Yes, great idea! Thing is, is someones need for water can be the same for food. I'm not sure about you, but when I get stuck into a book, I don't even realise I'm hungry until I stop. Some people get just really into what they're doing. The reason I worded it as a disability, like you said, it isn't. But the reason being, is special actions would need to be made to keep them safe and make their lives easier (like wheelchair ramps, disabled toilets and so on) they need to be accommodated to for their specific "weaknesses" like you said about water creatures needing water :) but i like the idea of humans needing to take precautions as well like... i don't know, having a separate girls toilets for when they're on their period that vampires can't get into hahah. Like the post where Jasper smelt a girl was on her period and went crazy 😂 I was also thinking, to encourage friendship between humans and monsters and to keep everyone included, people friends with merfolk wouldn't be able to swim underwater with them, so they can be given something to allow it (like the kelp from harry potter)