What is a Gravity Water Filter?

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.

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.

You can read Philip Werner's complete explanation on what a gravity water filter is here.