Why Should the MSR Guardian Water Filter Cartridge be Kept Wet?

If you own an MSR Guardian™ Purifier, you may be wondering why you’re not supposed to dry out its hollow fiber filter cartridge before storage. If the fibers dry out, they will “refuse” to accept water again. The pump will become hard to operate or may not pass water at all. The safety of the filter is not compromised—the fibers won’t crack and the pores in their walls won’t expand or constrict; they can still block pathogens. But the pump itself will simply stop working. If you have concerns about your filter cartridge being compromised, we recommend you perform the integrity test (instructions listed in manual). 

Unlike the MSR AutoFlow™ and MSR HyperFlow™, which are microfilters, the MSR Guardian is a purifier. This means it removes viruses in addition to bacteria and protozoa. To remove viruses (which are far smaller than bacteria and protozoa), the MSR Guardian had to be built with revolutionary hollow fibers. These fibers are made of special materials which happen to be hydrophobic (literally: “afraid of water”).

During the manufacturing process, we ensure that the filter is wetted properly, and it remains sufficiently wet as you use it—unless, that is, you purposefully dry it out. The MSR Guardian’s hollow fibers will stay properly moist inside the pump housing. Meaning, you should store the system as a sealed unit (pump head and clean side cover both screwed onto the filter housing). If the Guardian’s cartridge is left inside the housing, hollow fibers will stay properly moist, with no action needed on your part.

ALWAYS sterilize your MSR Guardian purifier before and after long-term storage to avoid mold growth and ensure fresh-tasting water. For sterilization instructions, please see the user manual. The user manual can be found on the Gaurdian's Product Page under the FAQs and Documents tab. 

For more information on this topic, you can visit our blog post.