Review: MSR Guardian Water Filter

The MSR Guardian is an amazing device that filters contaminants down to 0.02 microns. Most other filters filter to 0.1 – 0.3 microns. While these “normal” filters are fine for most applications they will NOT filter the ultra small organisms such as viruses. The MSR Guardian WILL filter most viruses and it can be used to filter extremely fouled water. If you do a quick internet search you should be able to find this filter for around $350.

The Guardian is portable and lightweight (only 17.3 ounces). It can filter 2.5 liters of water per minute. The Guardian pump filter is self-cleaning and about 10% of the pumped water is used to continuously clean the filter. The filter lasts for 10,000+ liters. A hose allows you to pump water from a stream other water source. The Guardian retails for about $350 and a replacement filter costs about $150. This filter can be used by backpackers or anyone that needs to filter a larger volume of water quickly. If you are in an emergency situation where the water supply was compromised then you should use a 0.02 micron filter such as the MSR Guardian. This is also an excellent choice if you travel to remote locations with questionable water quality.

Threads on the bottom of the Guardian connect to wide-mouth bottles such as Nalgene bottles. A duplex hose reaches from the filter to the water source. One of the duplex hoses is the water intake and the other is the flush line. About 10% of intake water flows over the ceramic filter to continually clean it. The cleaning water is then pushed out the flush line on the duplex hose. The clean, filtered water drops out of the bottom of the Guardian into a wide-mouth bottle.


  • Filters water to 0.02 microns (most other filters are 0.1 – 0.3)
  • Continuous cleaning as water is filtered
  • Filters high-volume of water quickly (2.5 liters/minute)
  • Hose allows easy access to water source
  • Portable and less than 18 ounces
  • Filter water directly to a wide-mouth bottle


  • Unit and filters are more expensive than other filters
  • Filter life good but less than other filters such as the Sawyer


If you want a serious water filter then this is one of two that I recommend. For a gravity filter consider the Sawyer Zero PointTWO. If you need to filter higher volumes of water quickly then the Guardian is an excellent choice.