I do run the Geigerrig system and I have had to throw out a filter because it froze on the last night on me of a trip in July. I didn't have it in my bag because who expects it to drop into the 20s overnight in the middle of July, even at 11,500ft. I do however also carry a Nalgene or Powerade bottle for adding some Mio to my drinking water. I almost never carry the bladder filled as most areas I am in have plenty of water. While the freezing issue is a concern, 95% of the time you should be able to predict when it might freeze overnight or not and plan accordingly. I have a quick disconnect so it'e not a problem to throw it in my bag. For the other 5% there is a reason that I carry some sort of backup in the form of tabs or drops in my first aid kit, which you could stretch by not purifying water before you boil it for food. Aron said that he carries an empty bladder for situations where they will be heading into areas where water will be harder to come by, but runs a Nalgene with a Steripen for all other cases. I plan on testing out both the Sawyer gravity system and the Steripen at some point this year. I also carry a mosquito head net to use as a pre-filter in all cases to avoid clogging and needing to back flush in the field.