How to Filter or Purify Water in Freezing Temperatures

Water filtration and water purification are as important in freezing weather as they are the rest of the year. Giardia, bacteria, and cysts don’t go to sleep when temperatures dip near or below freezing, nor do beavers, mice, deer, rabbits, and all the other animals of the forest that can contaminate the water supply with organisms that cause water-borne illnesses in humans. The only thing that does change is the effectiveness and convenience of different water treatments and purification methods.

What are the pros and cons of the water filtering or water purification techniques that backpackers normally use in warm weather, when temperatures get frosty and dip below freezing?

• Water filters that use hollow tub filtration technology like the Sawyer Squeeze, the Katadyn BeFree, Platypus Gravity Works, and others break when they thaw after being frozen, even if only partially frozen. Once this happens, there’s no way to know or test whether they’re still effective or whether they’ve been compromised.
• A pump filter like the MSR Guardian ($350) can withstand a limited amount of freezing/thawing and is a good option if you afford it. But other pump filters like the Katadyn Hiker Pro or the MSR Miniworks are ruined if they freeze.
• Ultraviolet purifiers like the Steripen can fail if their batteries freeze or lose power in cold temperatures. While lithium-ion batteries won’t freeze like alkaline batteries, their discharge rates can drop too low for cold-weather operation.
• Liquid chemical purification drops like Aquamira or liquid bleach can freeze and become useless.
• The reaction time of chemical purification tablets like Katadyn Micropur, AquaTabs, or Potable Aqua slows down in cold water, although they are not prone to freeze-thaw issues like their liquid counterparts.

Philip Werner gives a complete explanation on how to filter or purify water while in freezing temperatures, you can find the complete article here.