MSR Autoflow Gravity Filter Review

A gravity filter that can hold and treat up to four liters of water at a time, this water filter is a fast-acting water treatment method that is great for groups while backpacking or base camping.

Performance Comparison

Neck and neck with the Platypus Gravity Works the MSR AutoFlow comes in a nose behind, is the same price, an ounce lighter but scores slightly less in the ease of use category.

Reliability / Effectiveness

The AutoFlow treats for bacteria and protozoa, including the hard-shelled Cryptosporidium, but does not fully purify and treat for viruses. The lack of moving and electronic parts means it is unlikely to break in the field and is a very reliable treatment system.

This gravity filter has the same cartridge life and maintenance procedure as the GravityWorks; we suspect they have exactly the same filter unit. It lasts for 1500 liters, which is a large enough amount of water to last the average backpacker for quite some time. The suggested maintenance is to backflush the filter every other use or so. We discovered that when the filter has a lot of use in a group setting, it is best to backflush a full four liters through the filter for maximum efficiency.

The bag included with the MSR filter to hold dirty water has changed this year from a durable 200 Denier nylon to a 12 mil PU film bag and we believe this is not as durable, and we feel more comfortable dragging other filters along creek beds.

As with all hollow fiber membrane filters, except for the MSR Guardian that has been freeze tested, beware of letting the filter unit freeze. This can damage the filter without the user knowing it. Freezing can be prevented by bringing the filter unit into your tent at night.

Ease of Use

This is a very simple system. Scoop water from a flowing source into the four-liter bag (2 liter sized bags are also available), roll the top, and buckle the bag to a tree branch. Then hook up the hose and water comes squirting out the hose to the bottle attachment or can be flowed directly into a bladder, bottle, or pot. It should be noted that one of these additional vessels is needed, and a clean bag is not included with this system like it is with the similar Platypus GravityWorks. This means that if filtering into a bottle or pot, the filter needs to be attended and can't be left to do its thing while you set up camp like you can with the Platypus. However, if filtering into an MSR Drom bag or hydration bladder, then this is not an issue.

The bottle adapter on the AutoFlow can screw on to some types of bottles for ease when filtering (though it does not screw on to all types of bottle tops). However, screwing the adapter tightly onto a hard-sided bottle (like a Nalgene) traps air inside, and the water can't flow into the bottle. It needs to be left cracked or not screwed on tight, otherwise, the filter stops flowing; this is not an issue when filtering into another bag. We think that using the bottle adapter seems unsanitary in a group setting and prefer not to use it to fill our bottles. Switching the adapter from one bottle mouth to another could potentially spread germs.

We do think that the MSR version is easier to close. The roll-top bag is very simple to close, whereas the Platypus bags have a thick zip-lock type closure that can be very difficult to seal completely, especially if it is cold out and it just gets more difficult to close the more frequently it is used. The AutoFlow eliminates this issue with its easy roll-top.

The mouth of the MSR bag opens wider and is easier to fill than the Platypus bag as well. The only time this filter is troublesome is when the water source is small, trickling, and/or goopy. In this case, something like the LifeStraw or a pump like the MSR Sweetwater Microfilter would perhaps be a better option. The gravity filters work much better with flowing sources.

Another benefit that the AutoFlow has over the GravityWorks is that the bag comes with a buckle so that it can easily be hung from a branch. The GravityWorks 2L system comes with a buckle, but the 4L system does not.

Treatment Capacity

The dirty bag can hold up to four liters of water. It works quickly, so large quantities of water can be filtered in a relatively short period of time. This system is very conducive to treating water for groups or using as a treatment method for a base camp. Systems like the Katadyn BeFree and Sawyer Mini have a much smaller treatment capacity because the water needs to be manually squeezed through the filter with much smaller bags. Chemical treatments like the Aquamira Water Treatment Drops also have a smaller capacity overall, and can only treat 30 gallons per package versus the AutoFlow treats up to 1500 liters in its lifetime.

Speed

This filter works fast. In our timed test, it took exactly one minute to fill a liter bottle through the filter, which is the same speed as the Platypus GravityWorks. However, after a few days of heavy use, this filter will slow down significantly without backflushing. We found the Sawyer Mini had a similar problem and did not experience this with the Katadyn Gravity Camp 6L. Chemical treatments like the MSR Aquatabs have a much longer wait time to treat your water and can take up to 30 minutes to treat 2 liters.

Weight

MSR continues to strive for the lightest gravity filter on the market. The AutoFlow system switched out its filter unit for a more lightweight (albeit more delicate) filter unit and more recently lightened up its bag materials including a smaller buckle and lighter PU bag. It now weighs in at a svelte 10.9 ounces. This weight does not include the cap of the bottle adapter, which adds .7oz. The AutoFlow is now lighter than the Platypus system with the storage bag and all accessories but keep in mind the MSR system requires an additional vessel to filter water into, whether it is a bottle, cook pot, or hydration bladder.

It works especially well with an MSR bladder or an MSR Drom Lite bag (that can be used with a hose attachment to work as a hydration bladder). Remember to factor in this extra vessel to the total price and weight of this filter. The Platypus system is more of a complete system in that it has a bag included to filter the water into, however an additional vessel will be needed to drink from, either a bottle or hydration system. Keep in mind that if this filter is being used to treat water for a group, it is lighter than if each person carried their own filtration system. You can also save yourself 1.6 ounces if you leave behind the unhygienic bottle adapter and cap.

Best Application

This filter works wonders for treating water for a group of people or for being a water treatment method at a basecamp. However, it is also fast and light and comes in a 2-liter size that it can be used for a solitary hiker on the go as well. We believe all the gravity filters in this review are good choices for groups, especially the MSR, Platypus and Katadyn models.

Value

$120 is on the pricier side for a water treatment method, especially considering that you may need to purchase an accessory like a Drom Lite bag to go with this filter. The GravityWorks filter is priced the same but comes with slightly more water storage capability. Ultimately, we think this price is worth it because this is a reliable system that works very well, especially in group settings and treats a lot of water before it needs replacement. We think the Katadyn Gravity Camp is a slightly better deal at $90.

Conclusion