Best Answer: I would say no. I have had 5 rabbits. My buck is fathering 12 babies at the moment. I have never given my rabbits vitamins in their water. My first rabbit lived to be 9 years old.
It is possible to overdose a rabbit on vitamins.A lot of pet stores will try to sell you vitamins to put in their water. They just want your money. (Some are on the more expensive side) As long as you are feeding them a proper diet and ensuring they have plenty of fresh water at their disposal,pellets of rabbit food and hay they shouldn't need extra vitamins. Timothy hay is best for rabbits over a year old and Alf alpha hay is best for rabbits less than a year old. It provides extra nutrients that pellets alone don't provide. With a balanced diet, your rabbit will be fine without adding vitamins. Make sure you don't feed them too much of one kind of particular veggies or fruits as this can cause wet tail. Hope this helps.
I wouldn't recommend putting anything in their water. Often, animals that taste strange material in their water will simply stop drinking it. Just keep up a steady diet of mostly hay and fresh veggies and some pellets. See my source for some good info on rabbit nutrition, and if you have any more questions, you can always call your vet and ask. ;)