It's important to clean and sanitize your backcountry water filter or purifier before storing it during the off-season and winter months. A simple three-stage process involves cleaning the filter to improve flow rate, sanitizing it to kill microorganisms, and drying it before storing it until you're ready to use it again.

Step 1: Backflush Your Water Filter or Purifier

Many backcountry water filters and purifiers can be backflushed, meaning you reverse the normal flow of water through the filter element. This unclogs debris or contaminants stuck in the filter, flushes them out, and improves the filter's flow rate. Many filters and purifiers come with a hose or a syringe, like the Sawyer Squeeze that you can use to perform this backflushing operation. Others require you to “shake” the filter element, like the Katadyn BeFree when attached to a full bladder, to clean it.

If you've used your water filter or purifier recently, you only need to backflush/clean it a few times. If you haven't used it recently and the filter element is “dry”, it's best to run water through the filter in the normal direction to wet it out before commencing the backflushing operation.

Try not to apply extra pressure when you backflush the filter element because it can rip or deform the internal element, which may be paper, depending on the product you use. Sawyer claims their filters are pretty tough, but others are not, and I think it's prudent to be firm but gentle during the backflushing process.

Step 2: Sanitize the Filter Element

In this next stage, you need to sanitize the filter/purification element and kill any microorganisms that may remain inside. You don't want these to keep growing over the winter because they can permanently clog or damage the filter element. Different manufacturers suggest slightly different procedures, so check their website recommendations.

The two most common ways people sanitize their water filter/purification element are to flush it with a diluted bleach solution made with one capful of fragrance-free bleach per Liter of tap water. A few liters should do the trick. Filter these as you would in the field with raw water. Once finished, filter a quart or two of plain tap water through to remove any remaining chemicals so you don't get a mouthful when you start using the filter next season.

Alternatively, you can treat a liter or two of water with Aquamira drops or Katadyn Micropur tablets to sanitize your filter. These contain chlorine dioxide, which is an ultralight way to purify backcountry water sources without filtering. If you use one, you don't need to rinse your filter afterward, as the water you'll backflush or clean your filter with is completely potable. In fact, many city and town water supplies use chlorine dioxide to treat their tap water.

Step 3: Drying and Storage

Let your filter/purifier dry slowly and naturally by placing it in a warm, well-ventilated location, out of direct sunlight. After a week, move it to a drawer or closet in the heated part of your home. Come next season, it will be ready to use.

Note: Some manufacturers suggest slightly different procedures, so check their website recommendations. For instance, rather than letting your filter dry, some recommend storing it wet after sanitizing.

That's all there is to it!

Updated September 2026.

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