James -

your sweat rate could be next to nil. I have to bring 2 shirts to the gym to lift. we will have drastically diffferent hydration rates.

If you get thirsty, its too late. you need to be consistantly topping off liquids and cals to race distance. I can't imagine a 1/2 marathon with no water, let alone a 30k training run, no mater what zone your in. but, if it works for you, that's what counts.

I have a REI quickshot water bottle holder. Very small, enough to carry water for a 90 minute run (or stops at a water foutain) small pocket for the car/house key. doesn't bounce much, and I hate fuel belts