Like my post on Carrying Water in Winter where I touch on why I do not carry a bladder and drinking tube in the winter time – something to also think about is a water filter.
For the most part – almost all filters will freeze up in the winter time, if they are not properly warmed up by being kept close to the body, and in some sort of insulating layer. And if they freeze up, they are just dead weight, with extra weight now that there is the new addition of frozen water in the tubes and filter itself.
Another issue here is when water freezes, it expands – this could possibly cause damage to your filter as well.
I have a Katadyn Hiker Pro, and on my latest backpacking trip, decided to leave it behind because of this. I did decide to bring along some Potable Aqua water purification drops, if needed, but I did not end up using, as we had freshly fallen snow.
If you have the means to make fire, have a pot, and a bandana or something that can be used to filter out particulates in the water – boil it. Do not rely on your filter.
This post inspired by Bull in a China Shop (below).