It's been mentioned that bladders with drinking tubes can freeze. If you have one and get caught in the cold, empty the tube after each drink by blowing the water back into the bladder. It's not a cure all but it does help.
This also helps in hot weather as the water doesn't get hot in the tube.
So far as warm weather, it also keeps the water in the tube from leaking down the front of your shirt/coat. If there's any air leakage around the bite valve it drip and even can siphon. I don't usually blow into the tube but I do open the valve, pinch it, and hold it overhead so the water runs back into the bladder.
Tom
