Carrying water is rarely necessary here (it just doesn't get that warm very often...) unless you're running for several hours. For marathon training, I'd often plan routes that included just buying a cold drink (and maybe some chocolate :-) ) part way round. When I've done all-day or multi-day runs, where you do need to take some amount of clothing/emergency gear/food with you anyway, backpacks with a camelbak were perfect. Never had any trouble with keeping them clean, but I do tend to leave bite marks on the tube after a while. There is a bit of a trick to getting the water in there without any air, so that it doesn't slosh round on your back, but other than that they're pretty comfortable and I've run long distances in them