It really boils down to your personal hydration needs. If you have run 50+ Marathons you should have your hydration requirements down pretty well. That said...try to imagine being at altitude, heat, cold or whatever extreme condition and then double your time of exposure (at least double if this is your first PPM) at your regular level of exertion during a hard race. Then make the judgement call as to if you could go for 1-1 1/2 hrs with only 1 aid station. As said before, if you are an elite who is highly trained at altitude & Mountain running, you could chance it, if you are like 99% of the rest of us out there, bring a bottle!!! If you need it, great, if you don't run with it empty. Don't let vanity or the small weight issue leave you on the mountain pissed off that you didn't bring a stupid water bottle. Just remember to train with one you like for a few long runs.