"A crab needs water."
Translation:En krabbe behøver vand.
I think this is wrong. I was taught that "behøver" should be used with an adverb to describe something that you don't need. If you need something, it should be "har brug for."
This sentence should be "En krabbe behøver ikke vand" or "En krabbe har brug for vand"
Learned this in my Danish classes here in Copenhagen, correct me if Im wrong.
Yes, it looks like you are right. https://forum.duolingo.com/comment/4851830/When-to-use-beh%C3%B8ver-and-when-to-use-har-brug-for