The best system I've seen for water is riveting a bicycle bottle holder somewhere on a beam. Either the rear beam where it's out of the way, the base of the mast if you have an internal downhaul, or on the boom (this is MarkP boat, I know because he used duct tape to fix it .

Another option is to keep the bottle inside the rear beam, with bungees to keep it in place, works on my 5.2 but not on the Stealth where the beams are closed.