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Platypus GravityWorks Water Filter System

GravityWorks Water Filter Components
GravityWorks Water Filter Components

The Platypus GravityWorks Water Filter is a kit that includes all of the components needed to set up a gravity-based water filter system. It includes a water filter, hosing, quick-connectors, a handy hose shut-off valve and two 4 liter platypus hydration reservoirs for holding “dirty” pre-filtered water and “clean” post-filtered water. Having un-successively assembled a gravity system myself, it’s nice to be able to buy all the components at once and have them work out of the box.

Gravity-based filtration systems work by using gravity to force “dirty” un-filtered water through a passive water filter and in to a “clean” water container. It’s not quite as simple as that though. Water bubbles can form in the hose between the filter and the reservoirs and cripple the flow rate, the filter can require backflushing if you filter a lot of silty water, and it’s easy to cross-contaminate the dirty and clean parts of the system if you’re not really careful to keep them separate.

Gravity filter systems like this are very good to use if you need to filter a large amount of water at once and don’t want to have to pump it all through a filter or wait for your water while chemicals kill the microscopic bad stuff in it. When I say large, I mean anywhere from 6 liters for 2 people camping at night, up to 24 liters for an 8 person scout troop (or more), where you really want to make sure everyone has clean water. For myself, I usually filter 3 liters when I set up camp to get me through dinner and breakfast.

GravityWorks System hanging from a Tree
GravityWorks System hanging from a Tree

How it Works

Water is collected from a stream or river in the dirty reservoir, the one marked “DIRTY”, and then hung up in a tree from a hang strap. The dirty bag uses Platypus’ 4 liter (1 gallon) Water Tank style zip-lock style opening so it’s easy to fill in stream without having to scoop 4 liters of water up by hand. That’s a nice touch, really.

Attach the dirty platypus bag bag using the quick connect when you're reader to start filtering
Attach the dirty platypus bag bag using the quick connect when you’re reader to start filtering

The next step is to attach the end of the hose that feeds the filter to the bag marked “DIRTY”. This is done using a quick connect that prevents you from getting water all over yourself. Simply slide the male end into the female end and listen for the click.

The clean side of the hose is connected to the filter (note the direction of flow on the filter cartridge) and ends at a screw on cap to the clean bag, marked “CLEAN.” There’s only one way that clean water can enter the clean reservoir and that’s through this hose: the clean reservoir doesn’t have a zip lock opening like the bag marked “DIRTY”.

Clearly marked direction of flow arrows
Clearly marked direction of flow arrows

Once everything is connected, put the clean bag below the dirty bag and let the filtering begin. Once there are few inches of water in the clean bag, it’s important to lift it above the dirty bag, so that any air bubbles in the hose or filter element can bubble up and back into the dirty bag. This also serves to backflush the filter and prevent clogging. Once the bubbles stop, lower the clean reservoir and let the filtering complete.

Clean reservoir must be lower or downhill from the dirty one
Clean reservoir must be lower or downhill from the dirty one

From there, you can decant the clean bag into smaller water containers or use the hose to pour clean water into a cook pot. Platypus includes a flow regulator that you can use on the hose, but it’s easily lost: I just transfer the clean water to my 1 L water bottles or screw a regular Platypus bottle cap (not included in the kit) onto the clean reservoir.

Usage Tips

You don’t have to hang the dirty and clean bags from a tree branch: in fact, you’d be amazed at how difficult it is to find a single stubby branch, let alone two, that are strong and short enough to hang a reservoir from. Instead, you can simply position the dirty bag on a hill or rock, so it’s higher than the clean bag. Doing this can be advantageous even in tree country, because it’s a lot easier to lift the clean bag  above the dirty bag in order to backflush the filter and clear the line of air bubbles before each use.

When you’re finished using the GravityWorks system and ready to stow it in your pack, the best thing to do is to stack the two bladders, connect all the hosing, and simply roll it all up together. It will be wet, so stow it in an external mesh pocket on your backpack, preferably on the front of the pack so that it won’t drop on your pants as you walk. Platypus includes a lightweight mesh bag with the kit that you can use to hold everything together,  but an outer mesh pack pocket will serve the same function.

I also make a point to rinse out any accumulated muck (sand, leaves, etc)  in the bottom of the dirty bag before storage, so it’s reasonably clean before I use it the next time. After you’ve packed everything away, be sure to wash your hands with soap or clean them with hand sanitizer to prevent ingestion of bacteria or protozoa.

Flow Rate

No gravity filter review would be complete without some flow rate testing. On average, the Platypus Water Filter takes 45 seconds to filter a liter of water, which is pretty fast in my book, but I’ve done all of my benchmarks with stream water that has had suspended solids in it. The benchmark that Platypus publishes is much faster at 1.75 L / min, but I reckon that’s done with purified water which you’re unlikely to find in the backcountry. Either way, this is excellent performance and you can filter a whole lot of 1 gallon batches with the GravityWorks system in a relatively short period of time.

Roll the system together to carry in your pack
Roll the system together to carry in your pack


The Platypus GravityWorks Water Filter System is a very well thought out gravity filter system that’s good base camp or for couples or larger groups of hikers who need to have a large amount of water filtered quickly on the go. It’s also very well labelled and only fits together one way, the right way, in order to prevent cross-contaminating clean components with dirty components. Bravo to Platypus on the design; they’ve obviously incorporated a lot of field testing and product feedback back into the design and it shows. If you primarily hike solo or always carry your own filter, I wouldn’t recommend switching to the GravityWorks System. It’s a bit on the bulky side when it’s rolled up and has too much capacity for a single individual, but you certainly could use it by yourself if cost were an issue.


  • Works right out of the box
  • Clean and dirty reservoirs are clearly and permanently marked
  • Easy to backflush in the field (no sink required)
  • Impossible to accidentally put dirty water into the “clean” reservoir
  • Easy to fill zip-lock “dirty” reservoir


  • Inconvenient to use the GravityWorks reservoirs to drink from, so the system is basically dead weight when you’re on the move.
  • Be nice if the clean reservoir came with a regular Platypus screw-on cap.
  • Wish this was a purifier solution, not just a filter, so it could be used for international travel or in an emergency like a natural disaster.

Manufacturer Specifications

  • Effective against protozoa: Yes
  • Effective against bacteria: Yes
  • Effective against particulates: Yes
  • Effective against viruses: No
  • Effective against chemicals/toxins: No
  • Weight: 10.5 ounces (dry weight)
  • Width: 3 inches
  • Height: 9.5 inches
  • Filter media: Hollow Fiber
  • Filter Pore Size: 0.2 microns
  • Flow Rate (L/min): 1.75 L/minute
  • Filer Cartridge Life: 1500 Liters
  • Field Cleanable: Yes (backflush)
  • Water bottle adapter: No
  • Cartridge Replacement Indicator: No

Disclosure: Cascade Designs provided SectionHiker.com (Philip Werner) with a sample Platypus GravityWorks filter for this review.

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  1. I used a DIY system much like this. The one thing that I think is wierd is the “clean” bladder. Playtus makes a really nice 4L container called the water tank that has the screw top and the ziplock on the top of the container and has an expanding bottle which makes it stand up nicely. Seems like a much better contained to drip into.

    • Mark – Totally agree. I’m a little out of date with Platypus’ current line of hydration bladders. I stockpiled the freestanding, harder 3L bottles when they became scarce, and haven’t made the switch to the newer, softer bottles. The freestanding quality of Platypus bottles is/was one of their greatest conveniences for me, especially in camp. Glad to know that they have one in a 4L size, although I never trusted those zip lock closures for carrying water in my pack. Paranoid.

  2. Have you ever reviewed the Sterpin System and it effectiveness?

    • It’s up next. I have to get out with it first to test it out. But I can tell you right now, that you woun’t want to use a Steripen for a large group. Doing one 1/2 liter bottle at a time for a decent sized group doesn’t scale. It’s definitely a single user/single person solution.

  3. I’ve been using the Platypus GravityWorks for about 2 years and am an avid fan. The speed is more than fast enough for me. Just the thought of never pumping again overjoys me. The platypus drinking tubes will screw on to the clean bladder, it just doesn’t come with the package. I have plenty of them lying around – I personally don’t like drinking from a bladder. I normally carry a push-pull top for it, and not just a solid cap. All the Platypus stuff is interchangeable.

    The cap will screw onto a Seagrams, Canada Dry, or Coke product liter bottle. It will “almost” fit Dasani 1L water bottles. I have not actually tried a Coke brand bottle since I don’t drink Coke, but inferring from the Dasani and Canada Dry bottles, they should fit at least as well as the Dasani.

    I keep the clean bladder in the pack as a dry section capacity boost, but rarely actually use it (basically only for camping dry camps or >15 mi dry sections). I normally fill directly into my bottles. You have to leave the caps on loose so that air can escape as water fills the bottle. Obviously, you don’t have to do that with the bladders.

    In about 1000 miles of use (guessing 200 L), it’s never clogged once, and never let me down. I can’t say that for the pumps I used to use (First Need). I’m in and out of the water hole as fast as the pumpers or the Aqua Miraers. I like the ability to drink immediately. I’m usually camelling up on the first bottle while filling #2 and then refill #1 again and I’m off. When it’s raining, it’s a joy to fill the bladder and just stand quietly in the rain instead of being hunched over a stream getting soaked.

    I try to get water as clean as if I was using chemical treatment. The only water that I pump that is not crystal clear is Florida water, which frequently comes from ponds which are not so pleasant to drink from. I also carry either Aqua Mira or Iodine for emergency or when the water source is bacterially / virally suspect, which is basically any source I can’t see it shooting out of the ground from. I’ve also never “had” to collect dirty, silty, mucky water. Your dirty bladder looks pretty gunked in the pic.

    • Great feedback. I really like the ability to backflush the filter every time you use it. That is a clever trick and also helps get air out of the line. That’s probably why my DIY system never worked. (You know iodine doesn’t kill viruses – got to use chlorine dioxide instead)

  4. My fiancee and I use the Sawyer system. It’s a little more weight because their bags are made of a more durable material. Not sure the trade of is worth it if you are careful with your stuff. Filter works great like you outlined here for the Platypus version.

    Here’s my question: be it on the trail or in the morning before leaving camp, there’s the inevitable experience of needing to unload our packs to be able to get our bladders out for top offs (a logical solution to this issues seems to yet escape backpack designers). The gravity filter system seems like it should be a perfect option– filter directly into your bladder… while still in your pack. I know for us solving this problem would eliminate our most common on-trail inconvenience.

    Any thoughts on the feasibility of this using a gravity system? The hard part I see is that given a fully loaded pack’s inherent compression, even with gravity behind it, the dirty bag still ends up being the low pressure end of the system and the flow may not work.

    • That’s why people carry water bottles in their side pockets. Filling a water bladder in an full pack is a frustrating exercise because you have to basically have to repack you pack afterwards.

  5. I use the dirty bag and the filter but then I just have a bite valve on the end. I fill up with dirty water and filter as I drink on the trail. less parts, less weight, and simpler.

    I also made a small hose that attaches so I can use it to filter water for other people or pour water into containers for cooking/cleaning.

  6. Great review! I’ve been using the same system for a few years and have had no issues at all. I do wish the tops of the bags were more like the Giegerrig bladders with a slide mechanism to close and seal them off. It appears from the images that they still have the same ziploc style tops as mine. They don’t seal well for me. But overall, I love the system. Pretty light and packs easily.

  7. Why bother with the “clean” receptacle? Just attach your regular water bottles/bladder/whatever to the clean end of the system!

  8. @Early – yes, I know iodine is not a true kill-all, but it does have one advantage – it can kill the taste of pond water that stays even after filtering. That being said, i usually don’t carry it and haven’t used it in over 20 years – I carry the Aqua Mira instead.

  9. Nice review. These filters have been some the best designed and most reliable outdoor gear in my ever growing inventory. I’ve been using the previous version for over 1500 miles by myself or small groups with absolutely no problems. It gets carried in a dry bag so that in case of really cold weather, it can go in the pack or sleeping bag to keep from freezing. I carry a 12′-18″ strap with a buckle to hang the dirty bag from almost any branch, not just the stubby ones. A gallon ziplock bag makes a decent scoop for shallow water without mucking up the dirty bag.

    After filtering, I backflow about a quarter liter to keep something from drying in the filer and to help the sediment wash out of the dirty bag. Once home, I’ll backflush a couple of liters of water with some bleach to clean it out.

  10. I have been considering getting the platypus gravity works bags and hose sets without the gravityworks filter, and in it’s place using a Sawyer in-line .02 or .1; it looks like it should work assuming the hose fittings work on the Sawyer in-line fittings. That should make a pretty nice gravity system without the need for disposable filters.

  11. Update – when I first posted my replies about this filtering system, I was still using the original blue filter system. After three years of use, I decided I’d go ahead and replace the cartridge (and order the charcoal add-on filter for taste in Florida tannic water). When I got the new one, I was pleased to find out that the gray ended filters are almost 3 oz lighter than the blue ones. and the gray ends come off to shed another 1/2 oz if you so desire. So I must say, I like this thing even more now.

  12. Hey Alan from the hospital in Austin again.

    Phillip I have some amazing modifications to the Gravity Works for you. You can use the clean bag as your backpack water bladder, eliminating some dead weight. If you splice in a quick connect on the outgoing end of the filter hose, you can snap on a camelbak quick connect hose. Making sure to keep the clamp valve on the clean bag side and putting the female end of the quick connect on the dirty/ filter side, you will be able to detach the two parts of the systems without any water escaping.
    Three added bonuses come from this. One because the clean bag is staying in your backpack, all you need to do is put the dirty bag on top of your back pack as it sits against something, no need for branches or rocks at all. Two when you get to camp you can pull the bladder out, disconnect the drinking hose and you are still left with a hangable water dispenser with the working clamp still attached. Three if you put your quick connect near the output side of the filter and are again sure to put the female side towards the filter, you can disconnect the filter from the dirty bag with limited water loss just in case you need to bring the filter into your bag for cold weather.
    There is also some quick connect Fu to splice a pump into the whole system if you are in a region like mine where allot of water is really shallow.

  13. I purchased this item in 2015. I love it. I modified the tubes and connections so that the clean bladder could be used as a bladder to drink out of while on the move. It wasn’t very difficult at all. And for extra protection when I am in very questionable areas that require higher attention to having clean water, I will take and put a tablet in the clean water to kill any bacteria that the filter didn’t get.

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