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Hands-on Gear Review
Platypus GravityWorks Review
Cons: No separate storage for clean and dirty hoses, expensive, hard to collect water from small or non-flowing sources
Bottom line: A great, easy water filtration method for backcountry trips with groups.
Winning our Editors' Choice award, the Gravityworks churned up some surprising results in our lab. Taking the lead in our side-by-side tests when compared to other water filters in our fleet, we determined that it easily treats any amount of water, small or large, is incredibly versatile, and works well for a large group of people (or for a solo hiker on the move). Our initial thought was that this system would be too bulky and time-consuming for our quick pace, but we soon found out that this was the cream of the crop.
In fact, this one of the fastest systems for filtering water; it is the best option for filtering large quantities, is one of our lightest filter systems, and requires little to no maintenance. The filter lasts a long time before replacement (1,500 liters). The primary drawback to this system is that is more expensive than the average pump filter such as the Katadyn Hiker Pro or the MSR Sweetwater Microfilter. Also, it does not treat viruses like the SteriPEN Ultra or the MSR Guardian, so if you plan to travel around some very sketchy water, this may not be the filter system of choice.
This filter just barely beat out its closest competitor, the MSR AutoFlow Gravity Filter. This very similar system may work best for you, especially if you already have an MSR hydration bladder or Dromedary bag to use with it.
RELATED REVIEW: The Best Backpacking Water Filters and Treatment Systems of 2017
Our Analysis and Hands-on Test Results
This unique water purification solution allows for the ultimate storage and filtering device. It's available in a two-liter or four-liter size and has a capacity of eight total liters (four in the clean bag and four liters in the dirty bag). This is a huge bonus and allows for a constant, convenient, and adequate water supply for a campsite or for those making their way through an area that is lacking in an ample water supply. The Gravityworks eliminates the need for carrying a separate water container for clean water, which ultimately saves you weight and space. Fast and simple to use, you'll have easy access to potable water no matter the situation (unless you need to treat viruses).
The GravityWorks was our top scoring water purification system, earning our prestigious Editors' Choice award. See the chart below to find out where the rest of the filtration systems in our review fell in line behind this one.
The hollow fiber filter is effective against protozoa and bacteria, but not viruses. For what it does sterilize, this is a very reliable system. It is ideal for backpacking in North America where Giardia is the biggest concern, but would not be the best option for international travel.
The absence of moving or electronic parts means that it is less likely to break or malfunction. Be cautious of letting the filter itself freeze. This could potentially ruin the filter without the user realizing it. We protected against this by tucking the filter element in our sleeping bag on nights we were worried the temps would get below freezing.
The maintenance on this system is very low and the filter does not need to be replaced all that often. This painless process involves flipping the filter unit so that the direction of flow through it is reversed and letting at least ½ a liter of clean filtered water go through the other way. We discovered that when the filter is having a lot of use in a group setting, it is best to backflush a full four liters through the filter for maximum efficiency. You can just walk away and do something else while it is flushing, but don't forget to flip the filter back around when you're finished back flushing! This is nothing compared to scraping a ceramic filter like the MSR Miniworks EX or the complicated back-flush on the Lifestraw Mission.
There are two things to watch out for: do not puncture a hole in one of the bags, which would ruin the system, and don't let the filter unit freeze, which can damage the hollow fiber membrane. However, the bags seem very durable and in our long-term tests where we have used this filter extensively, we have not had an issue with this. It is possible that the MSR AutoFlow Gravity Filter would be more durable, although MSR has updated their materials and we're not sure anymore, but we have found the Platypus bags to hold up to a lot of hard use.
Ease of Use
This system is ridiculously easy to use, even more so than a lot of pump systems. You fill the dirty bag, zip the top, attach the hoses with the arrow on the filter pointing towards the clean bag, and set the dirty bag somewhere above the clean bag (it doesn't even have to be very high). This system worked fine with the dirty bag sitting on a rock and the clean bag on the ground, it does not need to be hanging from a tree to operate.
After you fill it and set it up, you can let it work its magic while you set up camp or eat a snack. One of our favorite things about the GravityWorks is that you can have a bag of clean water already filtered on-deck and ready for someone to just pour into their bottle of hydration system; you then have the dirty bag ready to refill right away. This makes getting water filtered for large groups very easy and quick. The Sawyer 4L Water Filtration System also has two bags to use for clean and dirty water.
We like that the dirty bag and clean bag are clearly labeled, and the dirty bag has an open zippered top, while the clean bag does not, so you will not accidentally mix them up and cross contaminate. The only downside is that the hoses are not as easy to keep separate. Since the dirty hose has the filter attached to it, they are easy to tell apart, but there is no convenient way to pack them to keep the hoses separated from each other.
Our main complaint is that the top can be incredibly difficult to zip shut, especially if your hands are cold from dipping the bag into a snowmelt stream. In our experience, this zipper gets harder to close the longer you own the filter. It closes like a ziplock bag but with a much larger and harder plastic seal. It can require some serious hand strength to zip shut so that it won't leak. The Autoflow and the Katadyn Gravity Camp 6L both have easy roll top designs.
The following chart shows you that the GravityWorks excelled in this category! Read on to learn why.
This filter excels at treating large quantities of water for groups or cooking. The 4L System can store and carry up to eight liters of water at a time, and the whole system can treat an entire gallon in under five minutes. It works very well to set up this system at camp and take water from it as you need it.
Other products that did well in this category are the similar gravity filters like the Gravity Camp and the Autoflow. If you are looking for something that is light and easy for a day out we'd recommend the Katadyn BeFree that only has a small carrying capacity, but provides instant filtered water.
This gravity system works surprisingly fast. We timed the filtration process in both the two and four-liter systems. We tried to make it as even as possible by raising the dirty bag so that the hose fell straight to the clean bag with no coil of hose on the ground, making the fall line the same for the tests. It took 1:50 for the entire 2L system to work and 3:05 for the 4L system. We also timed just a single liter moving through the filter, and that took exactly one minute.
This is less time than waiting for tablets like the MSR Aquatabs to work their magic and involves less work for the user than any of the pump systems. None of the pumps will provide four liters of treated water in under five minutes. Even the SteriPEN Ultra, takes 90 seconds per liter. If you do the math, it takes six minutes to purify four liters of water, not counting fill times in between sterilizations. Waiting almost five minutes to drink can seem like a pain, but in actuality, this GravityWorks system treats the most water the quickest and with the least amount of work.
Including the storage bag, the 4L system weighs 12 ounces, which is one of the lightest filters we tested, being beaten only by the Katadyn Gravity Camp and now the Autoflow has shed some weight and is a mere 10.9oz. Chemical treatments and compact straw systems like the LifeStraw and the Sawyer Mini are also lighter, but have a different purpose. This makes the GravityWorks a great choice for hiking and backpacking since it does not weigh you down.
Differences in the 4L and 2L Systems
Both the two and four-liter systems use the same filter and draw from the same general principle for using gravity to push the water through the filter. They both feature bags made of durable Platypus plastic and come with a shut-off clamp for the hose. So is the only thing different the size? No. Actually, there are a couple of notable differences, mainly in the configuration of the system. Here we list them for you so you can better decide which one will work best for you.
Since this system excels at treating larger quantities of water, it is well-suited to car camping or backcountry trips that will involve a base camp. Our initial impression was that it would not be as conducive to fast in-a-day backcountry missions where you want smaller quantities of water quicker, and do not want to sit around for five minutes waiting for it to filter. Then we tried it on our own hiking mission and felt that it took only as much, if not less, time to filter water through this system as with a pump. Even though the bags hold a gallon of water, you can fill the system just part way if you are in a hurry and do not want to carry extra water. Our final verdict: it works well in just about any backcountry situation where you would like to filter water, with perhaps the exception of really nasty shallow pools where scooping up goopy water would be difficult.
At $120, the 4L filter system is on the expensive side, which seems strange for such a simple system. It costs more than even the SteriPEN with its high-tech UV light. It does, however, include storage bags, which could cut your costs on another item and makes it a better value than the AutoFlow. This system is excellent to use and works very fast, so in our opinion, it is worth the investment, but expect to shell out a few more dollars for the luxury that the gravity system provides.
In the end, we felt that the GravityWorks was the best water treatment system available, and the one we'd recommend to friends and family for general use. If you are looking for one water filter that can serve your needs, whether car camping or backpacking, this is the one we'd pick. And, that's why it earned our Editors' Choice Award for the best water filter in our fleet.
You can purchase this versatile filter in either two or four-liter sizes. For lighter weight, get the small version; for more versatility and group camping, get the larger version.
— Jessica Haist
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