Platypus GravityWorks 4L Review: Filter a Camp Without Lifting a Finger
GravityWorks turns water treatment into a chore you can walk away from: hang the dirty bag, and four liters of clean water collect below while you set up camp. Two separate reservoirs keep contaminated and clean water apart the whole time. It is built for groups, basecamps, and family trips where everyone needs refilling at once.
What we liked
- Filters 4 liters hands-free in roughly two and a half minutes
- Separate clean and dirty reservoirs prevent cross-contamination
- Ideal for groups where one person refills everyone
- Quick-connects let you drink straight from the clean line
- Backflushes clean with the included adapter in under a minute
What to watch
- Bulky and heavy for solo trips where a squeeze filter wins
- Hose fittings can weep if the quick-connects are not fully seated
- Dirty reservoir needs thorough drying or it will mildew
In depth
How gravity filtration changes the job
Gravity filtration removes the physical effort from water treatment. You fill a dirty reservoir, hang it above a clean one, and the water moves itself through the filter cartridge. The trade is that it needs a place to hang and takes a few minutes to produce a batch, rather than delivering water on demand as you walk.
That trade is a good one in camp and a poor one on the move. Groups and families who arrive at camp needing several litres for dinner, washing and the next day's bottles will appreciate being able to set it up and walk away. A solo hiker who drinks through a squeeze filter while walking is better served by carrying a third of the weight.
The other advantage is hygiene. Because the clean reservoir is a separate container, water never needs to be transferred from a dirty bottle to a clean one by hand, which is where most cross-contamination happens with improvised setups.
Setting it up and getting the flow you expect
The setup is straightforward: fill the dirty reservoir at the source, hang it from a branch or a trekking pole setup, connect the hose to the filter and the clean reservoir, and let gravity work. The height difference between the bags is what drives the flow, so hanging the dirty bag higher speeds things up considerably.
Flow also depends on the cartridge's condition. A new filter moves water quickly, while one that has processed a lot of silty water will slow noticeably until it is backflushed. Backflushing with the supplied adapter takes about a minute and restores most of the original performance.
Hose management is the small detail that decides whether the system is pleasant. Keeping the hoses from kinking, and making sure the quick-connects are fully seated, prevents the weeping leaks and slow drips that make the setup feel fussy. A short length of cord to hold the bag at a comfortable height is worth carrying.
Keeping the dirty side dirty
Cross-contamination is the failure mode that matters most, because it silently undoes everything the filter just did. The clean reservoir should be treated as sterile: it touches nothing but clean water, clean hands and the clean end of the hose. The dirty reservoir and its hose never come into contact with it.
In practice this means handling the dirty bag first, filling it away from the clean container, and washing or sanitising your hands before you handle the clean end. Keeping the two containers physically separated, for example on either side of a table, is a simple discipline that prevents most mistakes.
The drinking valve on the clean line is convenient but also the most likely place for a mistake, since people put it in their mouth and then handle the dirty bag. Wiping the valve before drinking, and being consistent about which hand does what, keeps the system trustworthy.
Maintenance, drying and storage
The cartridge needs two things: regular backflushing and thorough drying. Backflush after every trip, and more often on a long trip with silty sources. Drying is what prevents mould, and a filter stored wet in a warm place will develop an unpleasant smell that can be hard to remove.
Draining the reservoirs, hanging them to dry inside out, and storing the filter cartridge dry with the caps off is the standard routine. Leaving water in the reservoirs between trips also encourages the plastic to take on a stale taste, which then transfers to everything you filter.
Freezing is the one thing that permanently damages a hollow-fibre cartridge. Ice expands inside the fibres and ruptures them, and a filter that has frozen should not be trusted even if it appears intact. In winter, keep the cartridge in an inside pocket and sleep with it.
Planning water for a group
Gravity systems make the most sense when you plan around batches. A four litre batch covers two people for a meal and evening drinks with some left over for the morning, so a couple of batches a day sets the rhythm. Working out your group's actual consumption on a short trip is more useful than any rule of thumb.
Water needs rise sharply with heat, altitude and effort, and cooking and washing add more than people expect. A camp that washes dishes and brushes teeth needs noticeably more than one that does neither, and it is worth deciding the policy for the group before the trip rather than after the water runs out.
Where a source is silty or algae-filled, pre-filtering through a cloth before filling the dirty reservoir dramatically extends the time between backflushes and keeps the flow rate usable. That one step is the difference between a filter that works all trip and one that needs constant attention.
When to choose a different treatment
For solo trips and fast packing, a squeeze filter is lighter, requires no hanging point and can be used while walking. The gravity system is a group and camp tool, and carrying it alone is weight you will feel on every climb.
For water where viruses are a concern, filtration alone is insufficient and chemical treatment or boiling is needed as well. A gravity system can still do the mechanical work first, which lets chemical treatment act more effectively on clearer water.
For emergency kits and winter trips, chemical tablets and a means of boiling are the reliable fallbacks, because they have no moving parts and cannot be ruined by freezing. Most experienced groups carry a filter system plus a small quantity of tablets as a backup, which covers both the likely and the unlikely failure.
Questions we get asked
Does it remove viruses?
No. The hollow-fibre cartridge removes bacteria and protozoa, which are the main risks in most backcountry water. Where viruses are a concern, add chemical treatment or boil the water as well.
How do I dry it properly?
Empty both reservoirs, hang them inside out to dry, and store the cartridge dry with the caps off. Drying is what prevents mould and stale tastes, and it also makes the cartridge last longer between replacements.
Can I drink straight from the clean hose?
Yes, the clean line has a valve for drinking directly. Treat the valve as the cleanest part of the system: wipe it before drinking and avoid handling it with hands that have just been in the dirty reservoir.
How long does the filter last?
With regular backflushing, it handles a very large volume over several seasons. Flow that never recovers after backflushing, on a source verified to be clean of debris, is the signal to replace the cartridge.