Have experienced all of the challenges mentioned above with keeping a bladder clean, filling it is a pain unless you take it out of the pack, and if it’s cold out, the tube easily freezes, Really sucks when you’re packing an animal out, needing water badly and can’t get at it because the tube is frozen. For those reasons, I switched to carrying Nalgene bottles this year. Exo makes an insulated Nalgene bottle holder, makes it easier to access, and they are much easier to fill and clean than a bladder. Early season I might still opt for a bladder because it’s so much easier to get a sip of water while you’re on the move, but if there’s a chance of freezing temps I’m taking the bladder out of my pack for sure.