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 teh 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.
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.
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”.
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.
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.
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.
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.
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.
- 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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