At least once a day, if not more frequently. Mine have both a water bottle for back up and a dish (a regular stainless steel dog dish). They seem to prefer the dish, and it's a lot less hassle for me to change it, so sometimes they get fresh water a few times a day rather than just once a day. Then again, sometimes Simon does goofy things like put his front paws in the water dish. I have no idea why he does this, but he doesn't seem to mind. Silly rabbit.