What kind of water filtering bottle can work under freezing point?

If you are winter camping in snowy conditions, there are several options for water purification: 1. Since you will be melting snow as your water source anyway, you can just continue to heat that melted snow past the boiling point for several seconds. This will kill any contaminants. 2. You can take the melted snow (make sure the water isn't too hot) and filter it with a pump filter as you normally would. With option one, you carry less weight in gear (ie no filter to carry around), but you will require a little more weight in fuel (but not all that much). The downside of this option is that the water is safe, but not necessarily totally clean of debris. Even in snow conditions that look pristine, there always seems to be a good bit of debris in the melted snow. For some people this is totally fine, and for others it is a real turn-off. With option two, you have to carry the weight of the filter, but you get very clean water. This option can be a little more troublesome in practice than in theory...reason being that there will be some water/moisture left in the pump filter after each use, which will subsequently freeze. This can damage the filter, and even if it doesnt, it means you will have a little trouble getting the hot water through the filter at first, because it has to melt through all the ice inside. The best solution to this (if the debris bothers you) is to perhaps bring a small bit of cheesecloth or something similar (coffee filters are too slow) and pour the melted snow through the cloth filter before consuming...this will catch almost all the noticeable particles. Also, if you find yourself with a frozen water pump, the only way to clear it is to stop and heat some snow/water and pump it through it...believe me, I have tried putting it inside my coat, blowing warm air through it, etc. and none of it helped, but putting warm water through clears it in a matter of a few seconds.

Why carry a filter bottle thats bulky and heavy and when it freezes the filter will be useless. Just melt some snow in a pot, the boiling temperature will kill and organisms and if you are at a higher altitude there is no need to worry about organisms in your water.