Platypus GravityWorks Water Filter (4L) Review

Platypus GravityWorks Water Filter Review

The Platypus GravityWorks Water Filter is a complete and well-integrated water filter that includes all of the components required to set up a gravity-based water filter system. Gravity water filters are good for filtering several liters backcountry water at once for consumption by families or groups. It’s basically a batch approach to water filtering and eliminates the need to pump or squeeze water through the filter one liter at a time. The Gravity Works system 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. It’s all color-coded and very well documented making it a great system for people who aren’t familiar with water filtration or only do it occassionally.

Specs at a Glance

  • Weight: 12 oz / 340g
  • Flow rate 1.75 liters/minute
  • Filter life: 1500 liters
  • Filter media: Hollow fiber membrane
  • Filter pore size: 0.2 microns
  • Filter efficacy: remove 99.9999% of bacteria and 99.9% of protozoa including giardia and cyptosporidium
  • Temperature range: Above 32 F/0C (do not freeze)
  • Contents: quick disconnect fitting, clean reservoir with clean cap, filter cartridge, dirty hose (12 in /30 cm), clean hose (48″ / 122 cm), shut-off clamp, clean side clamp, storage sack w/ instructions printed inside
  • Field cleanable: Yes (backflush)
  • Water bottle adapter: No
  • Cartridge replacement indicator: No
  • Field filter integrity test: Yes

Gravity-based filtration systems work by using gravity to force the “dirty” un-filtered water stored in a reservoir through a water filter and into a “clean” water reservoir. 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 cleaning 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 careful to keep them separate. Platypus has factored all of those issues into the Gravity Works design though, so they’re easily and safely addressed.

Platypus has labelled the clean and dirty bags separately so you can’t confuse them
Platypus has labelled the clean and dirty bags separately so you can’t confuse them.

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. You can also use this gravity filter setup for one person, but it’s really intended for use by couples or a group use. Platypus sells a lighter weight 2L version of the GravityWorks system for personal use.

The hose attachments are also color-coded so they can’t be mixed up.
The hose attachments are also color-coded so they can’t be mixed up.

How it Works

The GravityWorks System comes with two reservoirs, one labelled DIRTY and one marked CLEAN so you can’t confuse them. 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 strap. The dirty bag uses a Platypus 4 liters (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. Simply find a small stream pour over and fill it up.

The first step is to fill the dirty bag with raw water from a stream or pond.
The first step is to fill the dirty bag with raw water from a stream or pond.

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 color coded 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 hose to the filter can only plug into the dirty bag, so you can’t cross-contaminate your clean bag
The hose to the filter can only plug into the dirty bag, so you can’t cross-contaminate your clean bag.

The clean side of the hose is connected to the filter (note the direction of flow arrow on the filter cartridge) and feeds into the clean bag, marked “CLEAN.” There’s only one way that clean water can enter the clean reservoir and it’s impossible to misconfigure.

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 good to lift the clean bag 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. If you do this for a minute every time you use the filter, it will maintain a good flow rate. Once the bubbles stop, lower the clean reservoir and let the filtering complete.

The direction of flow is also marked on the filter element.
The direction of flow is also marked on the filter element.

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 also includes a cap for the clean bag; so you can simply cap it off and save the water for use later.

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 which has an attached sheet of instructions to refresh your memory if you’re out of practice.

The mesh carry sack has a printed set of instructions sewn inside
The mesh carry sack has a printed set of instructions sewn inside.

I also make a point to rinse out any accumulated muck (sand, leaves, etc) at 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 the 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.

More Gravity Filter Systems

Integrity Testing

If you ever become concerned about the safety of the Platypus GravityWorks Filter and wonder if it’s still working, you can field test the filter element by blowing into the clear hose to see if air passes through it (it shouldn’t). For example, it’s important to keep the filter from freezing in temperatures below 32 degrees Fahrenheit/0 degrees Celsius. If you think the filter has been compromised by freezing you can test it right away.


The Platypus GravityWorks Water Filter System is a very well thought out gravity filter system that’s good for couples or larger groups of hikers who need to have a large amount of water filtered quickly on the go. It’s also well labeled and only fits together one way, the right way, in order to prevent contaminating clean components with dirty water. 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.

Disclosure: Cascade Designs donated a gravity filter for this review.

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Last updated: 2022-05-16 17:42:05

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