Gravity Fed: Water Seeps Through Filter to be 'Cleaned'

Procuring clean water in the wilderness can be a pain. Pumps are hard work. Purifying tablets require a long wait. But last week, on a trek in northern California, I simply scooped some water from a stream and hung a bag in a tree.

The venue was the Lost Coast Trail, an ocean-hugging route where rivers pour out of green mountains and empty right into the sea. My water-filtering product of choice, the GravityWorks Filter from Platypus, gave our group near-instant access to drinkable water anywhere on the hike.

Gravity Water filter.jpg

As its name says, the GravityWorks Filter counts on nature’s primal pull (gravity) to coax water through a filter, no pumping required. The product, a system of tubes, water bags, and a filter cartridge in the middle, lets you grab untreated water then wait for gravity to do the work.

This system is not new, and we reviewed it in 2010 when Platypus called it the CleanStream Gravity Filter. A new name (GravityWorks Filter) and tweaks like a smaller filter and an overall reduced weight (from about 14 ounces to 10.5 ounces) are among the upgrades.

To operate the GravityWorks you fill the system’s “dirty” reservoir bag with lake or river water. Hang that bag in a tree or simply hold it up. Gravity does its thing, and water seeps out of a hose on the bottom, coursing through rubber tubing before entering a filter.

Clean water flows out the other end, slipping through a hose and collecting in the unit’s “clean” reservoir bag, ready to drink. The whole process takes just a couple minutes. There is very little effort required, allowing you to fill, hang the bag, and relax as water is dripping through from dirty to clean.

Gravity filter in use.jpg

GravityWorks Filter in action on California’s Lost Coast Trail

The GravityWorks’ filter unit has a pore size of .2 microns. That’s enough to eliminate bacteria, protozoa, and other “bugs” that may taint fresh water. It is not effective against viruses, but for most wild places that is not a worry.

Platypus quotes a filtering speed of 1.75 liters per minute, which was about what we saw on the Lost Coast. The unit costs $110, and it is made in the USA. Platypus cites 1,500 liters as the life of the filter, which can be replaced.

In a backpack, the GravityWorks folds and packs up fairly small. Stack the reservoir bags together, coil the hoses, and slip the filter unit in between — you’ll have a tidy water-cleaning system always at hand no matter where your trek may lead.

—Stephen Regenold is editor of Connect with Regenold at or on Twitter via @TheGearJunkie.

California lost coast trek.jpg

Scene from Lost Coast Trail

Posted by Bill Puckett - 04/02/2012 12:06 PM

I’ve used this system successfully, but I didn’t like the “zip” closure on the bags. After a couple of trips, the closure refused to close…at all. I replaced the dirty bag with an MSR bag and have been happier. The filter works well and a gravity feed system is the simplest and easiest I’ve found so far.

Posted by Jerritt - 04/02/2012 01:26 PM

It would be great to see this tested again in an environment with more sediment in the water. I really want to try one of these out, but have heard they don’t do so well when the water has significant particulates. (Of real interest in northern lakes in the late summer or fall.)

Posted by Stephen - 04/02/2012 02:29 PM

I just bought the filter, snipped the line on my water bladder and added the filter in there. Now I filter as I go. Only one bag in my pack so it’s lighter, and I know whatever swamp water that goes in there is clean before it hits my mouth. It’s also easy to backwash when things get dirty, just blow in the mouth piece.

Posted by Brett - 04/02/2012 08:20 PM

I know Making Your Own Gear (MYOG) is not the intent of this blog, but $110? Seriously?

I made my own with some hose from Home Depot, and filter, a Nalgene bottle and a Silnylon stuff sack. It cost me about $45 and mine weighs 6oz. Search the web for “MYOG Gravity Water Filter”

Posted by Jared - 04/03/2012 05:54 AM

Thanks for the cool idea Brett. I also think $110 bucks is a bit ridiculous for two plastic bags and a filter.
I’m gonna look into this MYOG Gravity Water Filter idea. Sounds like a really cool and fun thing to do.

Posted by Lance - 04/03/2012 06:35 AM

We’ve been using the MSR Gravity filter for a couple of years. Hands down the best backpacking purchase we’ve made.

Posted by jpea - 04/03/2012 09:18 AM

well, obviously they saw a need where people were making their own and realized that some folks didn’t want the trouble – voila :)

Posted by jason - 04/06/2012 05:36 PM

Interesting comments. A huge fan of MYOG, and it is true that it is often much cheaper, but I also agree with “jpea” that there is nothing wrong with having it available (and more expensive) for people that just want it all made and ready to go. I could make a synthetic ultralight sleeping bag similar to the Ultralamina for about $60 bucks, but I’d rather just pay for it and have it show up at my door in a nice stuffsack.
My favorite MYOG is armwarmers, calfwarmers and kneewarmers made out of my old calf-high wool socks!

Posted by Tyler - 12/05/2012 05:15 PM

Awesome read and great find!!! My favorite water purification system, Purificup, has been getting some awesome reviews….check it out

Posted by Ryan - 01/02/2013 05:22 PM

I bought mine at Dicks sporting goods for $44.98. It was on sale plus 25% off couldn’t pass it up!

Posted by John - 01/07/2013 03:51 PM

The author needs to learn the difference between FILTERS and purifiers. This is NOT a “water purifying system” BUT a filter. HUGE difference!

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