For the past 10 years, the Platypus GravityWorks water filtration system has been my primary method for treating water in the backcountry. When it comes to backpacking water treatment, we need a solution that is effective, reliable, and reasonably fast, without taking up too much space or weighing us down on the trail. Essentially, we need all-around performance. In this review we'll evaluate the GravityWorks water filtration system and how well it performs in the backcountry.

The GravityWorks water filter is all designed around a .2 micron hollow fiber filter cartridge.

Platypus GravityWorks Design

The Platypus GravityWorks water filtration system consists of 2 Platypus style water containers – a dedicated and labeled dirty and clean bag with a hollow fiber filter cartridge in between rated at .2 microns. The dirty bag has a heavy duty zip type opening to easily fill the bag from a water source and a convenient webbing strap attached to the top, allowing one to easily carry the bag back to camp or hang from a height to filter (a quick release buckle also makes this easy). An auto shutoff quick connect is integrated into the bag just above the bottom, handy for trapping larger debris. When the hose leading to the filter is disconnected from the dirty bag, water will not flow out – handy for transport or for storing water overnight when you need to sleep with the filter due to sub-freezing conditions. When the hose leading to the filter is connected (just insert until you hear a click), the flow will be activated.

To disconnect, one depresses the release button on the dirty bag to free the hose. Both the dirty and clean side hoses connect to the filter element itself with hose barbs that fit snugly, but are not difficult to remove or reconnect. The .2 micron cartridge is sufficient for most backcountry water filtration needs in North America, but is not effective against viruses and does not feature any type of carbon filtration to improve water quality or reduce heavy metals, etc. – Platypus does offer a separate GravityWorks carbon element for about $30 that could be spliced into the system if desired. For a deeper dive into water treatment considerations and what's required to treat what, see our backpacking water treatment guide.

The hollow fiber cartridge is rated for up to 1500 liters with a 1.75 liter per minute speed, and frequent backflushing is suggested. The clean side tubing is connected to a screw top cap which connects directly to the clean bag, also featuring a webbing strap but sans the zip type opening of the dirty bag. Along the hose in between the clean bag and filter is a shutoff clamp that allows one to control the flow of water with one hand.

The system is available in several configurations: a 2L size containing 2 X 2 liter bags and including their push/pull adapter, and a 4L size as tested here with 2 X 4L bags for up to 8 liters of storage, as well as a 6L system. The 4L system, shown in this review, is listed at 11.5 ounces. Although not currently on the Platypus site at the time of this writing, you may also be able to find a 2L bottle kit, with a 2L dirty bag and both the Platypus push/pull and bottle adapters – this system is listed at 9.5 ounces. The price is around $135 retail with individual components available for purchase if needed. A new / replacement cartridge will run you about $75.

Impressions & Field Performance

In the field I’ve found the system very easy to use on the trail and at camp. The system packs bulky, but fairly well by sandwiching the filter between the two bags and rolling everything together – and I choose to store the system in the outer mesh pocket of my pack for quick access on a lunch break. Filling from a source is easy. Disconnecting the dirty bag from the system, you’re able to grab 4 liters of water from a sufficiently deep source by opening the zip top and as I found is easiest, using a back and forth side to side motion to fill the bag with 4 liters of water in just a few seconds. Zipping the top shut forms a usually water tight seal (double check...wouldn’t trust it in my pack), and with the auto shutoff quick connect sealed (since the system is disconnected) you can easily carry the bag back to camp using the strap if needed or even store the bag full overnight.

After using the cartridge for an entire summer with sometimes pristine, sometimes not water I’m down to about .75 liters per minute after a fresh backflush – a full bag hung at 6’ with the clean bag on the ground takes about 5:30 to filter including the purge process. For reference, the dry weight of the system is 11.05 ounces (both bags, hoses, new filter, clean side cap) and around 14.7 after use with nothing more than a cursory shake to get rid of some residual water. The filter unit alone is 2.2 ounces new, but gains a little weight after use – 3.25 to 3.55 ounces or so depending on how long it’s had to dry. The clean bag which I personally sometimes leave behind to save some weight weighs about 3 ounces. Once you snap the system back together filtering is easy, just hang the dirty bag on a convenient tree, rock, or simply hold it above the clean bag (the higher the better) to filter and let gravity do the work.

Speaking of the filling process and the dirty bag – this is the only failure I’ve experienced with the system. On one trip I arrived at camp late, and set off to find water in a small stream. It was late in the year and quite dry, so the water source was very shallow. Scooping was difficult, but eventually I was able to fill the bag…only to find that it wasn’t filtering water. Apparently, during the filling process and due to the shallow water the quick connect on the dirty bag had filled with small pebbles and debris. Despite attempts to clear the debris via headlamp with the limited tools on hand, and despite seemingly being able to clear anything visible the valve just wasn’t working when the other side was connected – no way to filter water and perhaps it had been damaged on the first attempt to connect the system prior to the debris being removed. Luckily, I’d thrown in a Swiss Army Knife at the last minute for the trip and using the corkscrew, I was able to forcibly remove the workings of the valve (the spring and seal) from the quick connect housing.

It was now possible to connect the system together again and filter water to get through the trip without boiling – I just had to do without the auto shutoff feature of the valve for the rest of the trip. Moral of the story – the quick connect has moving mechanical parts that can possibly jam or malfunction – if it’s a shallow water source, use a scoop like a mug or cookpot to fill the dirty bag, and then sanitize that by boiling in it the next time you use it.

Using both bags can really get you a lot of camp capacity – filter into all your containers, then fill the clean bag, then fill the dirty bag and you could head back to camp with over 8 liters of water. One nice feature is the ability to use the system like a faucet as well. By filtering into the clean bag, you can potentially then remove the hose from the clean side of the filter and utilizing the shutoff clamp, have clean water on demand. I’ve also done the same by hanging the dirty bag, albeit at a slower rate since it has to pass through the filter.

With the large amount of capacity the 4 liter system can handle I found this to be more than I needed solo. In solo situations, I left the clean bag at home and filtered directly into my hydration reservoir and bottles. One trick that made this easier and better during the day while hiking was with the use of a quick and homemade quick disconnect system. By using a set of quick disconnects, with the auto shutoff (optional, but nice to have) spliced into my hydration system where the hose exits my pack and the opposing connector on the end of the GravityWorks system, I’m able to filter directly into my hydration reservoir without having to undo my pack…most of the time. On occasion my pack is cinched up too tight (I lay my hydration reservoir at the top of my pack horizontally) and I may need to loosen some straps to get the flow going. In any event, it’s much easier than the alternative.

Platypus has a couple similar solutions with their universal bottle adapter and their push/pull adapter, but you have to remove your bite valve. If you'd like to setup a quick connect system Platypus used to offer a quick connect kit but it has apparently been discontinued. You can however find alternative quick connect components at Amazon. For bottles, I just fill those directly from the hose although you can use the bottle adapter above as well if you prefer to go that route. In any event, if you do go with just the dirty bag beware of cross contamination – it can be difficult to completely isolate the clean side hose from dirty water that will get on the outside of the dirty bag and Platypus suggests keeping the system together as a whole to avoid this possibility. In my case I pack the clean side as separate as possible on the outside of my pack, and prior to filling any container rinse the end thoroughly with fresh filtered water similar to the manufacturer suggestion of rinsing the clean filter hose barb when using the clean bag as a camp water source and without the clean side filter cap.

When filling bottles, I also like to run the hose down and then raise the clean output side upwards so there’s a bend in the bottom of the hose, creating a drip stop if any dirty water were to run down the outside of the hose. The Platypus adapters have the benefit of packing with a little more peace of mind from any cross contamination. For groups of two and especially above, the extra capacity of using both bags becomes more reasonable and welcome. One of the great things about the system is that it works great off the shelf – or in any number of ways if you’d like to customize it specifically towards your needs.

But, a lot of talk about the process and not about the water which perhaps is a good sign. The end result is clean water, and lots of it, without a lot of effort and fairly quickly. I have found a few water sources where tannins remained, as expected, but if this is a concern or you’d like to further polish the water you drink you can always splice the optional carbon element in. The filter won’t remove viruses – use something else or combine with chemicals / UV if this is a concern for your destination of choice. In my case, the stock element and system is all I need for the mountains.

Care and Maintenance

As with most water filters, you’ll need to protect the filter cartridge from freezing and from drops. Here in the Rockies, I’m often worried about freezing temperatures on most nights so I always sleep with the filter in my sleeping bag, inside a Ziploc. You could keep the entire system together, but considering I often had the dirty bag full and ready to filter for the next morning this wouldn’t work in my case, in addition to all the space that the even empty bags and hoses would take up. Therefore, I have always disconnected the filter and slept with just that – Platypus provides a small clean side cap that you can slide over the clean barb to help prevent any cross contamination (honestly, shaking the filter out well and drying on my shirt seems to prevent any drips).

The clean side cap is very easily lost however, so keep an eye on it unlike myself with my first one…I was lucky enough to get some spares from Cascade Designs. To help with the issue, I really feel like there should be two caps for each side of the filter, but permanently attached to the filter itself to prevent loss…this would make the freezing / cross contamination issue easier to deal with. Gently shaking the water out, drying, using the cap, and a rinse of the clean side barb with freshly filtered water in the morning prior to reconnecting the clean side hose however has worked for me, but for 100% cross contamination prevention you’ll have to keep the system all together at all times.

You’ll want to be careful of dropping the filter as well and Platypus included 2 foam bumpers that help as a nice touch. No matter how careful you are though, there are always those moments. Forget your filter outside at night and aren’t sure how cold it really got? Maybe that accidental bump was too much? With many other filters you’ll just be guessing. However with the GravityWorks you can test it with a manufacturer approved method which is more unique.

To perform an integrity test you simply backflush at least half a liter of water by raising the clean bag higher than the dirty bag, then remove the clean hose from the bag and attempt to blow air in a reverse direction through the filter. Watching the dirty side section of clear tubing, if you’re blowing a steady stream of bubbles, the filter is damaged and cannot be used. I’ve used this method in the field and at home when those types of moments happen – the filter has always checked out ok and without a doubt it’s great for peace of mind. My hands down favorite part of the system.

Speaking of backflushing, Platypus suggests doing so (again simply by raising the clean bag above the filter and allowing clean water to flow through in a reverse direction with the dirty bag open or detached) every 2-4 liters. The process is easy and fast. Being lazy perhaps however, I simply do so when I notice flow rate decreasing and this is definitely not every 2-4 liters. They also suggest purging air from the system when you first start to filter water by running clean water again against the grain by raising it above the dirty bag until all air bubbles are gone from the line – in reality, I’ve done this a few times but mostly find I don’t have to worry about it.

After your trip, you can sanitize the filter cartridge by running a weak bleach solution through the system as detailed in the user manual – the solution that remains within the cartridge should keep the filter fresh for the next excursion.

Packed size of the GravityWorks water filtration system. I like to keep the filter in an outside pocket of my pack for easy access during the day.

Conclusion

After using the GravityWorks system for my backcountry water filtration needs over the past 10 years, the system has turned out to be a reliable workhorse, and thus far nothing else on the market has given me a compelling reason to consider taking something else for my backcountry water treatment needs. My absolute favorite part of the system is the quick and easy filter integrity test that can be used prior to a trip at home and in the field – since like most other filters in this category you can’t expose to cartridge to shock or freezing temperatures, there will always be those borderline moments. And with the GravityWorks you can be sure instead of guessing (or replacing what could still be a good filter) as with many other popular filters on the market.

You'll need to maintain the filter after your trip, but by choosing decent water sources, maintaining the cartridge, and backflushing regularly you can get quite a bit of use out of the system before the flow slows enough to warrant a replacement cartridge.

The system is a bit bulky and I learned the hard way to protect the quick connect on the dirty bag from debris, and the system does trend toward the heavy side. However in my case, the speed, convenience, and ease of use have exceeded any drawbacks in the field. The Platypus GravityWorks filtration system retails for around $135. Check it out here at REI Co-op as well as here at Amazon.com.

Editor's Note: This review was originally published in Issue 25 of TrailGroove Magazine. You can read the original review here featuring additional photos, a list of pros and cons, and our rating of the GravityWorks Water Filter from Platypus.