MSR AutoFlow XL Review

The AutoFlow XL gravity filtration system, which, aside from scooping up your water and hanging the bag, requires zero hands-on work to filter 10L of water in one sitting. It's our favorite for basecamps, large groups, and whenever large quantities of water need to be filtered.

Water Quality

The AutoFlow XL is capable of removing all the critical biotic and particulate substances that you might find in water drawn from rivers and lakes in the backcountry. The 0.2-micron hollow filter cartridge will rid your water of stinky substances, protozoa, and bacteria. We enlisted the help of experts from SGS Labs to do third-party lab testing, which confirmed these claims to be true. Results show the filter is capable of eliminating 99.9% of bacteria and protozoa. It was only able to remove 72.2% of viruses, but it is not designed to remove these extra-small organisms, so the 72% is more like a bonus. We tested this while group camping on the Gunnison River ripe with high levels of sediment and contamination of protozoa and bacteria that could potentially make our group sick. Thankfully, like most places in North America, viruses were not a major concern.

It's important to note that, like all the filtration systems tested in this review, the pore size is not small enough nor ionically charged to remove viruses, heavy metals, pesticides, or microplastics. So, if you plan on traveling to areas where this type of pollution is rich, this is not the filtration system for those trips. However, anywhere in North America or where these pollutants are not typically found in water sources, it works well.

Ease of Use

Setting up the gravity system is easy peasy. To collect water, the reservoir has a roll-top architecture that requires you to either plunge it into lake water or hold it sideways across running water. The downside of such a huge bag is that it's really difficult to collect from shallow and stagnant water sources. Tall banks require you to hover over them to try and reach the water. You don't always know what your access will look like, so it's better to be prepared for a bit of everything.

Once the water is collected, simply roll the top down and clip it onto a very sturdy hanging point; the 10-liter reservoir filled with water weighs about 22 pounds. You can also place the filter on a sloping hill, though the flow rate will decrease dramatically. From here, clip in the tube, attach the filter in the correct orientation (as per the picture), and then connect your receiving reservoir. The set comes with an attachment for a standard wide-mouth (think Nalgene) bottle. While we appreciate this attachment, we learned that it can only be used when the bottle is upright. The attachment can't be screwed on completely since air can't be vented out, which prevents water from flowing in. Another favorite that we like to filter into is our MSR DromLite Bag, which has the option for a tube plug-in attachment.

Overall, the setup is more cumbersome than other squeeze bottle systems, but pretty easy for a system that filters 10 liters of water at once. Since this is a gravity filter, the only thing you need to do is set up the system by filling the reservoir and hanging it so that gravity can do the work.

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Durability and Maintenance

This gravity system offers a high level of durability with only a little bit of maintenance. The filter itself is one system without any moving parts or complexities. This makes it less likely to fail in the field. The bag is composed of a thicker plastic composite that seems resistant to punctures and tears. When filling up the full 10L, we were a little worried about the seams splitting, but the RF welding is super strong and reinforced enough to uphold the weight. On the underside of the bag is a 1000-denier flat base that allows you to set the bag down on rocky or spiky surfaces without worry. The filter itself is also quite durable and built to withstand falls from 7 feet high. Just be sure to avoid freezing, as the cartridge will be deemed unusable if it does freeze.

While on a group camping trip with 20 high school students, a few of the autoflow systems that we had on hand began to reduce the flow significantly. At first, we were a little concerned as this was our only way of water filtration. However, when we simply flipped the filter around on the tube to backflush the system, it started to run at the initial rate again. While they do recommend only a half-liter to flush the system, we'd recommend filling to the half volume of the bag (about 4 liters), then backflushing it with the full amount. It's also important to backflush after every significant use to ensure the filter stays clear….especially in turbid water. After we ensured this type of maintenance, our filtration system remained reliable and efficient. This filter works for about 1500L before it needs to be replaced, according to MSR.

This burly bag can hold 22lbs of water. It also has a puncture-resistant denier fabric layer on the bottom, preventing abrasion and scuffs.   Credit: Amber King

A look at the clip that secures the bag to the anchor point. While the plastic is questionable, it sure is burly enough to hold this weight.   Credit: Amber King

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Treatment Time

We love this system because you just need to load up the bag, hang it high, then let it do its work. When measuring treatment time, we filtered a liter of water three times, then averaged how long it took to filter one liter of water. We did find that filtration times were faster if we could get a straight-ish line from top to bottom, giving gravity its best chance. In the field, we didn't really think about this as much, because we'd simply set it up first thing in the morning and walk away. By the time we finished breakfast and were ready to head out on a hike, we'd fill up and be on our way.

Treatment time is also affected by the clarity of the water. With normal tap water, we measured one liter to take about 2 minutes. With more sediment in the water, the flow rate dropped to about 4 minutes and required many backflushes. This was a pain when trying to filter 10 liters. Flow rate would vary depending on how full the bag was. The fuller the bag, the faster the flow; as the bag emptied, the flow rate decreased. But since we had lots of downtime in a group setting, we typically just walked away and had a reservoir of clean water waiting for use when we came back to check it. In general, this is one of the slowest treatment times we observed between all the gravity filters and other filtration systems. However, when testing it for use in a group setting, where time wasn't of the essence, it worked perfectly.

Weight and Packability

The components of the system are all stored in a convenient bag that takes up very little room in a backpacking backpack. From the point of view of a backcountry guide who typically carries more backup gear for a group, this system proves to be very convenient.

It packs easily into cracks and crevices while the weight is minimal. The bag rolls up, with the receiving reservoir either being a water bag that you might bring along a water bottle or a dromedary. All in all, it's lightweight and packable.

Should You Buy the MSR AutoFlow XL?

The quality and lightweight characteristics of the AutoFlow XL make this system well worth the price tag. The gravity-fed system produces high-quality filtered water, is highly durable, and is very easy to use. The Autoflow XL is also super practical, especially if you're looking to hydrate a larger group for an extended trip into the backcountry. The 1,500-liter capacity translates to about 150 uses for a group of ten people. If you're considering the best option for group filtration, this gravity system should be at the top of your list. It's the perfect filter for large groups or guided use.

What Other Backpacking Water Filters Should You Consider?

The MSR AutoFlow XL is a 10L gravity filtration system that is renowned for its easy setup and large capacity. While it does require regular backflushing, especially in turbid water, this is true of nearly every gravity filter out there. However, 10L may be overkill for 3-4 people. If you're interested in another gravity system in a similar price range that would be great for a smaller group, like a family of four, check out the Katadyn Gravity BeFree 6L. This system requires less maintenance and offers the same ease of filtration with a little less capacity. And if you're looking for a gravity system that is more affordable, check out the LifeStraw Peak Gravity 3L. This filter has one-third less capacity but remains durable and easy to use.