Lago, I just want to point out that this can be quite a polarizing topic on the internet. The opinions range from 'toss him in the pool' to 'Never never ever get a rabbit wet or you are torturing your rabbit and need to be reported to animal cruelty'.
Personally, I've never seen a need for it. I don't feel like my bun isn't happy/complete because he doesn't have regular access to a swimming pool. That said, if he needed it, I would attempt a shallow butt bath. I really feel like it's up to a good bun owner who knows his pet. I understand that the extremes are trying to prevent a bun from drowning. I like to give people the benefit of the doubt.
Other topics that are sensitive: Meat rabbits, Breeding in General, outdoor vs indoor, trancing.
I only tell you this so that you are not alarmed when someone from the internet rakes you over the coals, as I once was.
I would welcome reasonable, polite discussion on any of these topics, but that doesn't happen much in cyberspace. This board
is the best one out there for discussing all aspects of bunnies.