This is kind of new fangled to me... When we got rid of the little wooden kegs we carried water in and went to the little round metal canteens I thought WOW!!!! Much later learned to put surgical tubing into the CBR cap of a 2QT bladder upside down on my ruck and I was high styling... So the whole camelbak thing sounded pretty good. I picked up a surplus carrier and a excess 3l bladder. The question is.... other than water... What else is safe to put in them?