SectionHiker.com Backpacking Gear Reviews and FAQs 
A gravity water filter system uses gravity to force water through a filter so you don’t have to squeeze it manually or use a pump to push it through. The advantage of a gravity water filter system is that you can process large quantities of water without much effort. This is beneficial if you’re hiking with a partner, with your family, or in a large group. If you had to wait for everyone to process their own water, you’d be there all day.
| Make / Model | Type | Capacity | Reservoirs |
|---|---|---|---|
| Platypus Gravity Works 2L | Filter | 2L | 2 |
| Platypus Gravity Works 4L | Filter | 4L | 2 |
| Platypus Gravity Works 6L | Filter | 6L | 2 |
| Katadyn BeFree Water Filtration System 3L | Filter | 3L | 1 |
| Katadyn BeFree Water Filtration System 6L | Filter | 6L | 1 |
| Katadyn BeFree Water Filtration System 10L | Filter | 10L | 1 |
| MSR Trail Base Water Filter Kit | Filter | 2L | 2 |
| Sawyer Gravity Water Filtration System | Filter | 4L | 1 |
| CNOC Vecto and Versa Flow Gravity Kit | Filter | 3L | 2 |
| CNOC Vecto and Versa Flow Gravity Kit | Filter | 2L | 2 |
| MSR AutoFlow XL Gravity Filter | Filter | 10L | 1 |
| Lifestraw Mission Gravity Water Purifier | Purifier | 12L | 1 |
| MSR Guardian Gravity Purifier | Purifier | 10L | 1 |
You can buy gravity water filter systems off the shelf or assemble your own from components. Most off-the-shelf gravity filters include a multi-liter reservoir (with a hanging strap) to hold raw unfiltered water that you’ve collected, a water filter or purifier to process your water, and all the required hosing to connect the components. Some like the Platypus Gravity Works Gravity Filter System also include clearly labeled “Dirty” and “Clean” reservoirs so you can store the filtered water and not confuse it with raw water that must still be treated.
Units that only have one reservoir for use as a “Dirty” bag often come with a valve that lets you decant clean bottles of water as needed, rather than collecting it all at once in a clean reservoir. This can be handy in base camp situations so people can get a refill whenever they need one or if you use water bottles instead of a reservoir to carry your clean water.
Homegrown gravity filter setups use a dirty bag, clean bag, filter setup but may also require extra hoses and adapters to make the components compatible with one another. That’s the advantage of buying an off-the-shelf gravity water filter system from one manufacturer: you know it’ll all work together.
Most commercial gravity filter systems come with water filters that remove protozoa and bacteria like Giardia, salmonella, and cryptosporidia. But you can also find gravity water purifiers that also remove viruses like the high volume 12L Lifestraw Mission Gravity Water Purifier or the 10L MSR Guardian Gravity Purifier. These are good for international travel or places where viruses in the water supply are a concern.
While gravity filters and purifiers are very convenient for group use, many people also like them for personal use since you can filter all the water you need for camp use if you have a clean reservoir to collect it in, while you take care of other camp chores like setting up your tent, hanging a bear bag, or collecting firewood. For individual use, I’ve found that units with a 3-liter reservoir size, like the CNOC Vecto and Versa Flow Gravity Kit, are the best volume for your clean and dirty reservoirs. This gives you enough water for most of your camp needs and up to 6 liters of carrying capacity if you want to have to do a long water carry or dry camp.
Most of the water filters or purifiers that come with commercial gravity filter systems can also be used as squeeze-style filters for personal use, including the BeFree Filter or Versa Filter included in the CNOC Gravity Kit listed above. Look for filters that screw directly onto the dirty bag if you want to use them in a Squeeze-style setup. This is a good way to stretch your dollar if you want to use the same filter in a group and a personal water filtration/purification kit.
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Once you go gravity, you never want to go back! Have converted several hiking buddies once they experienced my 3L BeFree.
I use the Platypus 4L system for canoe camping and it works great. Last year I added another “clean” bag to the system so I filter 8L each time. It has been working out great.
I am a water filtration junkie and have used many different style filtration systems. For my purposes, I have totally moved away from pumps and squeeze products in favor of gravity. I use the Platypus filter with about 3 ft of tubing and a 2 liter dirty bag filtered into Smart Water Bottles.
The Platypus filter is a quick filter and easily cleaned. I also take care to filter water through a bandana into the dirty bag or avoid filtering turbid water. I always take care to filter the cleanest water possible through the filter itself. The idea of taping the bottom of the bag and adding grommets for support seems like something I will try in the spring. I personally have never had a Platypus bag failure….but I have seen a couple folks on the trail with bag failures. Bottom Line: I want to put the least pressure possible on my filtration system to avoid bag tears and filter clogs. And I always carry Chemical Purification as backup.