Your bunny should always have a fresh supply of clean, cool drinking water. I prefer to use chlorinated water as it has been purified, resistes the growth of algae in bottles and dishes, and is supposed to keep the rabbits healthier. I have always used chlorinated water with no problems ever.
Your rabbit does not need anything else in its diet besides the pelleted feed, hay and water. Treats may be given occasionally in small amounts-but remember they are just treats-nothing more.
There are certain herbs that can be given to your bunnies for certain illnesses and conditions. Here is a list of them and their uses: Herbal Remedies for Rabbits.