Water treatment and purification are as important in cold weather as they are the rest of the year. Protozoa, bacteria, and cysts don’t go to sleep when temperature 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.
In winter, when you have to melt snow to make drinking water, the most convenient and foolproof way to purify your water is to boil it. But what about if you backpack in cold weather when temperatures are intermittently near or below freezing? This is the time when many three-season water treatment and purification methods become inconvenient to use, unreliable, or fail altogether.
- Gravity and pump filters like the Sawyer Squeeze, the Platypus GravityWorks, or the Katadyn Hiker Pro are prone to clogging or cracking when they freeze and thaw (they don’t have to freeze all the way through to fail, mind you.)
- 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 bleach can freeze and become useless.
- The reaction time of chemical purification tablets like AquaTabs or Potable Aqua Iodine slows way down in cold water, although they are not prone to freeze-thaw issues like their liquid counterparts. There’s also some evidence that the effectiveness of chlorine dioxide and iodine drops in cold water, despite long contact times.
So what is the best water treatment solution when backpacking in the early spring or late autumn, the so-called “shoulder seasons” when temperatures straddle freezing?
Boiling certainly works, but it does require that you carry more cooking fuel. Technically, you only need to bring your water up to 160 degrees Fahrenheit to kill water-borne organisms, but since that’s difficult to know without bringing a thermometer, you’re probably best off bringing it up to a visibly gentle boil. While using a stove is probably faster, a wood stove or campfire can be good weight-saving options, particularly in the evenings when you have time to kill.
Another fuel-saving option is to bring the temperature of your water up to the point where its warm to the touch, pour it into a one-liter water bottle, treat it with a chlorine dioxide water purification tablet like a Katadyn Micropur, and stick it in your sleeping bag or an insulated water bottle cover to insulate it while the chemicals purify your water…just as they would in warmer temperatures.
The best option is to use a Steripen if all of the water you need to treat is in liquid form, as long as you carefully babysit the batteries and keep them warm using your body heat. One of my readers, Ben Weaver, wears a Steripen Opti on a lanyard around his neck at all times to keep the batteries from freezing. I think this is an excellent strategy although I’d still recommend having a backup if the batteries fail. The other advantage of using a Steripen is that it takes a lot less setup time than heating your water in a stove, so it’s good when you’re on the move.
While these tactics work for neutralizing organisms in cold water, they won’t be effective if you need to remove chemical contaminants from your water like heavy metals or fertilizer. There’s really no option other than bringing a mechanical purifier like an MSR Guardian or General Ecology First Need in that case, although freezing of the unit is still a concern.Editor's note: Help support this site by making your next gear purchase through one of the links above. Click a link, buy what you need, and the seller will contribute a portion of the purchase price to support SectionHiker's unsponsored gear reviews, articles, and hiking guides.