When I hiked the John Muir Trail, I used a redundant system of an MSR Hyperflow Filter and Aqua Mira (chlorine dioxide) to purify my drinking water. It wasn’t long before I stopped using the filter (except in situations where the water was particularly murky) and relied almost exclusively on Aqua Mira because let’s face it—filtering water is a real pain. But now Mountain Safety Research (MSR) has developed a new filter they call the Guardian Purifier that makes filtering water a little bit safer and a lot easier.

Physical water filters have three distinct disadvantages over a chemical purification system:

  1. A filter is not as effective against viruses and smaller protozoa (like the feared Cryptosporidium).
  2. A filter must be cleaned.
  3. A filter adds more weight to your pack.

But MSR has addressed two of these shortcomings with the soon-to-be-released Guardian Purifier.

Handling Viruses

MSR is billing the Guardian as “the world’s most advanced portable purifier” and that comes with the claim that this filter is an effective method to keep viruses from getting into your drinking water, thanks to the medical-grade hollow core fibers that do the filtering. Viruses just can’t get through (although actual spcs on micron size are not provided).


By the very nature of what they do, filters get dirty, and to remain effective, they must be cleaned. In the case of the HyperFlow, it should be cleaned (also known as “backflushed”) once for every eight liters filtered. On my hike, I drank upwards of two liters a day, which meant I should have been cleaning my filter every other day. The process is a little complicated and, if you’re not careful, it’s really easy to lose essential pieces, rendering the device useless.

Here’s a video that demonstrates the process for backflushing the HyperFlow (note how many times you’re not supposed to do something):

By contrast, the Guardian Purifier uses 10% of the the water oumped through it on each stroke to flush any contaminants back out to the source. End result: no backflushing necessary.


It’s hard for filters to beat the weight of two small bottles of Aqua Mira, and there aren’t any specs listed on the Guardian Purifier site, but the Guardian looks to be around the same size as MSR’s MiniWorks, which weighs 16 ounces (455 grams). However the MiniWorks uses a ceramic filter, so the Guardian with its hollow-core fibers might be a little lighter.

Other Advantages

  • The HyperFlow came with a warning to not let it freeze (which can happen when hiking the High Sierras in June) because that can damage the device’s filtering fibers. But the Guardian has been designed to withstand freezing. It’s always nice to worry about one less thing.
  • They HyperFlow has a filter life of 1,000 liters, but MSR lists the filter life of the Guardian at 10,000 liters and will last for upwards of ten years.
  • Lastly, when I used the HyperFlow, it took me about 1 minute and 45 seconds to filter a liter of water, but MSR says that the Guardian Purifier can filter 2.5 liters of water per minute. And although that sounds about 2.5 times faster, they also claim that the HyperFlow can filter three liters a minute, which was definitely not my experience. Field testing may be in order here.

The Guardian Purifier will be available from MSR beginning in January 2016. I’m looking forward to giving it a test run.

Update: One other downside the Guardian Purifier has: Cost. It’s set to retail for $350, but if it performs as well as promised, it’s a worthwhile investment.

Images via MSR and GuardianPurifier.com.


Written by Tom Fassbender

An amateur hobbyist, expert generalist, and outdoor enthusiast who recently traveled around the world with his family.

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