Home / Gear Reviews / Water Filters and Containers / MYOG: A Gravity-fed Water Filtration System using the Sawyer Mini Water Filter by Nathan Taylor

MYOG: A Gravity-fed Water Filtration System using the Sawyer Mini Water Filter by Nathan Taylor

$75 MYOG Gravity Fed Water Filter System
$75 MYOG Gravity-fed Water Filter System

I have used hand-pump water filters like the First Need or the Katadyn for years, believing them to be the only “real” option for filtering out cryptosporidium, giardia and other bacteria from the water sources in the Pacific Northwest where I hike. But I’ve been forced to consider other options in an effort to move towards lightweight hiking and backpacking.

Chemical and Ultra-Violet Water Purification

Chlorine dioxide tablets or drops are a good alterative except for the waiting time before you can consume the water. Many people have also found that the tablets did not always dissolve as expected. Ultra-violet water treatment solutions depend on whether the UV lamp is working and whether your backup batteries (which are not standard) are still good. But neither the chemical or UV treatments actually filter the water, leaving unappealing floaters in your bottle. If a water source is stagnant, you are still left with an unpleasant swill of technically drinkable but unenjoyable water. This was a deal-breaker for me.

The one option that I kept coming back to was the Sawyer Mini filter. The Sawyer Mini is a true revolution in lightweight water filtering. Weighing in wet at about 3 oz, it is the lightest true water filter on the market and is highly flexible in how you choose to use it. The advertised method involves squeezing the “dirty” water through the filter. It certainly works but many Sawyer users will tell you how the included bags have failed.

Gravity-fed Water Filters

Sawyer, Platypus and others also sell a gravity-fed system with the filter in between the “dirty” bag and the filter bag. Rather then depend on mechanical squeezing to supply pressure to the filter, gravity can do it with less stress on the physical components if you are willing to wait a bit longer. However both Sawyer and Platypus’s solutions are surprisingly expensive for a 2L set-up.

Pressure can be calculated using the equation P=pgh, where P equals pressure, p equals density, g equals gravity and h equals height. The operative variable is really just height in any gravity-fed water system. The diameter of the tube or the amount of water in theory does not make a difference. Increase height to increase pressure. In reality, the friction of the fluid passing through a tube does act to reduce this. A simple figure to remember is that every five feet of fluid height (excluding friction) results in a pressure of 2.2 pounds per square inch (PSI). This is the force that will push the water through the Sawyer.

The basic components of my MYOG Sawyer-based gravity filter areas follows:

I wanted the dirty squeeze bag to be easily suspended without ripping out the bottom of the bag. To do this I decided to reinforce the holes with metal grommets and then thread nylon string through them so that the weight would be distributed over all four holes. The Sawyer bags were selected because they are very light and inexpensive for the volume of water they can hold.

Reinforce Reservoir corners
Reinforce Reservoir corners with (yellow) duct tape

Directions

Start out by finding the bottom of the squeeze bag where the bag part ends and the expansion baffles begin. Reinforce all four corners with some duct tape which will act as reminder that this is the dirty reservoir.

Drill holes in the corners
Drill holes in the corners

Then drill a hole on each side of the bag through both front and back expansion baffles. Fit one side of a grommet through a hole, fit the other side of the grommet on where it emerges from the bag and give it a couple whacks with the grommet tool to bend the grommet into shape. Repeat three more times.

Thread the nylon string through the gromets
Thread the nylon string through the gromets

Lastly, thread the nylon string through the grommets. You should also put grommets on your clean bag, in case your dirty bag becomes compromised and you need another bag to suspend.

Next set up the inflow tube. I chose to use the 5/16” outer diameter tubing rather than the much less expensive 3/8” outer diameter tubing because it’s less than half the weight (1.7 oz) . The thicker tubing is more kink-resistant and less than a quarter the cost ($3 versus $13).

Cut a five foot section of tube, put the tube section through a tube clamp, plug one end to the Sawyer filter and the other end to the blue inline adapter from Sawyer (see parts list). The blue adapter fits the Sawyer bag and also has a neoprene washer.

Use Sawyer bag cap to draw a circle on the fine-mesh nylon bag
Use Sawyer bag cap to draw a circle on the fine-mesh nylon bag

Use the Sawyer bag cap to draw a circle on the fine-mesh nylon bag and then cut inside the line by 1/16” to 1/32″.

Fit both pieces of mesh inside the threads of the blue screw-top adapter. This mesh acts as a large particulate filter and keeps any floaters from reaching the filter and clogging it. Very fine particles, such as glacier silt, will go through so if you are using water that is cloudy with silt. Allow it to settle in a collapsible bucket before filtering. Cut out a couple of extra mesh circles and keep them in your “extras” kit just in case you lose the ones in the adapter.

The last section is the outflow side. The Sawyer adapter kit comes with a screw-top piece (blue) and a screw-in piece (grey). The grey piece does not fit in any normal bottle so you have two options: buy another Sawyer adapter kit and toss the grey parts, or buy a Tornado Tube.

The Tornado Tube is red in this picture.
The Tornado Tube is red in this picture.

I chose to go with the Tornado Tube which is actually a kids’ toy but it works great in this application. The grey adapter will fit in one side and the other side will screw onto pretty much anything: Sawyer bags, standard water bottles, Platypus reservoirs, etc. You can see the red Tornado Tube in the assembled picture above. Use a 2” section of tubing to connect the outflow end of the Sawyer filter to the grey Sawyer adapter screwed into the tornado tube.

Cut the top off a standard 1L water bottle and use that as a container for all the filter parts
Cut the top off a standard 1L water bottle and use that as a container for all the filter parts

I cut the top off a standard 1L water bottle and use that as a container for all the filter parts and the Sawyer bags. One advantage to using part of a bottle is that you can use it as a scoop if your available water is in a low-flow seep and you can’t just dip your dirty bag in to gather it. It will also prevent the Sawyer bags from getting punctured.

Filtering Speed

With the dirty bag suspended over the filtered bag by the full five feet of tubing, I was able to filter 2L in an average 139 seconds in three trials. I also tested with the Mini right under the dirty bag so that pressure from gravity was minimized. Three trial runs in this configuration resulted in an average time of 207 seconds, proving that in this case, gravity is your friend.

Fully assembled, including the 1L bottle container, my filtering system was 8.4oz and cost $75.
Fully assembled, including the 1L bottle container, my filtering system was 8.4oz and cost $75.

Construction Cost

Fully assembled, including the 1L bottle container, my filtering system weighs 8.4 oz and cost $75. That cost included many redundant or extra things. I did not need: 10′ of tubing, but that was the length it came in. I also did not need 12 tube clamps, but a single clamp was $5, so for twice the cost, I got extras in case I lost or broke one. The mesh bag also has lots of space to cut out more filter circles. Go in with a friend and make two filter set-ups to split the costs and extra materials.

Other options to add to your MYOG gravity filter:

I ended up adding the quick-connect fittings right above the Sawyer Mini on the inflow tube. They add a convenient way to unhook your filter from the hose when you are setting things up or packing it away.

All finished, my gravity fed water filter system weighs 2 ounces less than a Platypus GravityWorks Water Filter System and about costs about a third less. But making your own lightweight gear, that is a priceless experience.

BIO

Nathan Taylor lives in Portland, Oregon and enjoys the great variety of hiking climates available in the Pacific Northwest.

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28 comments

  1. Thank you. I was planning on building a similar set up. Since gravity hasn’t always been my friend (I’m recovering from surgery after multiple wrist fractures), this gives me some direction.

  2. First thing to do when using the Sawyer filters is to ditch their bags. I’ve never had one last more than a few trips before a tear/leak starts near the top. They should just cut down on their costs and skip bags all together and pass the savings on to us.

    Use the newer platypus platy bottles or evernew bottles.

  3. Nicely done step by step guide. And you retain the squeeze option

  4. I think that Tornado Tube bottle adapter is a home run. Got to get me one of those!

  5. I do a DIY gravity Sawyer feed like you Philip, but have a twist.

    I buy two Platypus 3L Hosers (~$25), and discard one of the hoses.
    The bag with the drinking tube goes into my backpack for clean water, like a normal camelbak, and the tube-less hoser is the dirty water bag and it can be capped for transporting dirty water if needed.

    Since the hoser bags already have a hanging ring on them, a simple carabiner will work to hang it from a tree, and it just feeds direclty into my backpack. And those bags are tough!

    Total weight is similar to your setup, ~8oz, but that also includes my while-hiking drinking container.

  6. Problem is,, the First Need Deluxe is a Government proven Water Purifier…Yours is not. My First Need cost me $75.

  7. I am with Philip, do not mind the few floaties, have been using my SteriPen Adventurer Opti for 4 years now, varied location, Grand Canyon, Yellowstone, up in some great Utah hikes, for the most part these are 6 or 7 day trips. Do carry extra set of batteries, find they will last at least 10-14 days of use for a single person. Easy to tell if the UV light is working, though may need to shade the unit a little in the bright sunlight to see the bulb to make sure it is on. Fast, light, easy. As a back up, take some Aqua Mira, but have not had to use yet, but just in case.

  8. Cool write up. I just bought some parts to do something similar. I got a Platypus 3L bottle as the ‘dirty’ bag because it wasn’t much more than the hose, and a Platypus (?) shut off valve for the end. I was going to splice in the Sawyer Mini and also the a Platypus Charcoal filter (though the charcoal filter can be eliminated in an emergency, since it does have to be replaced every 1000 gallons or so). The dirty bag can be filled with using the Steripen funnel to get any floaties out. For packing light, I may replace the 3L Platypus with a 2.5L USWE bottle, though I’m still looking for something with a wider mouth or opening that may be easier to fill in the field (i.e., MSR Dromedary, etc…).

  9. This what I use for my sawyer mini to make a gravity fed system. The good thing is the Reservoir opens nice and wide at the end so it is easier to fill. We just fill our 1liter bottles that we carry anyways but you could add another 2l reservoir of your choice.

    Platypus GravityWorks 2.0L Dirty Reservoir Replacement Kit $19.95 http://www.backcountry.com/platypus-gravityworks-2.0l-dirty-reservoir-replacement-kit

    Platypus GravityWorks/CleanStream Hose Kit $19.95
    http://www.rei.com/product/813801/platypus-gravityworkscleanstream-hose-kit

  10. I don’t think anybody makes an easier dirty bag than MSR’s AutoFlow Gravity. Unfortunately, you have to buy the entire filter system to get the bag (which is bigger and heavier than ultralighters are interested in anyway, but we’re not all ultralighters, eh?). It has a large roll-top opening, great for filling, obviously not suitable for carrying water in your backpack. Perhaps someone else makes a rolltop dirty bag? The strap on the MSR bag is also really handy for wrapping around a tree trunk, making it much more versatile than a mere beaner.

    Since I already have an MSR Gravity system, I hope to replace the airlock-prone MSR filter with a much-faster Sawyer filter. The Sawyer SP122 (half gray, half blue) filter works quite a bit faster than the Mini, although I haven’t been able to test them side by side. The Sawyer gravity system has a great flow rate and the fill opening on the dirty bag is better than a squeeze bag, but pales compared to the MSR rolltop bag.

  11. My problem with these squeeze mini setups is that the dart on the mini isn’t good for back-flushing (one of the best things about the squeeze line). If you try to back-flush using the above setup typically the tube will blow off on the clean side because the tip isn’t darted.

    I use a simpler setup with the Sawyer Squeeze original (yes, it’s .8 oz heavier). It’s setup like so from the top:

    2L bag dirty bag+ sawyer squeeze + tornado tube + 2L clean bag

    Fewer parts, and you can just invert and squeeze the clean bag for a quick back-flush if need be.

  12. Love the innovation-knowing I’ve chopped/cut and run a variety of options with Platy/Sawyers – in line and elsewhere – I’m thinking for @$25 more (or a few good beers) you should just get the full Platy Gravity Works set up (a bit more weight I know…but you get 4ltrs and no construction work)…I don’t like the dirty water bag zip top on it though – should be like the 3ltr zip: so have played with exchanging the 2 both w/ benes and trade offs of course. Have to say that neither Platy setup works well as a straight inline IMHO. I’m onto drops these days but love my 3 ltr Platy Zip as storage and the gravity works system when I bring my kids et al…they can’t get past the floaters…again awesome innovations and ideas…thx…

  13. Super article. I was frustrated by how slow the mini was and had not thought of making a conversion. I goofed around a little and found… 1) There are already points to put holes in the 2 Liter Sawyer bag and a hot soldering iron is the easy way to do it. Seems plenty strong. 2) I loved the pre filter idea but the simplest system is to keep the mini filter screwed onto the dirty bag and just attach a 5 foot tube to drops into your clean bottle. You can be in business for only tubing and nylon string. Hard to beat that price.

  14. Philip,

    Do you still prefer the Sawyer Mini over the bigger Squeeze?

    Maybe I’m lazy but the only filter I’ve used so far is the Mini. I’m finding that refilling the 1 or 2 liters can be tiresome because of the slow flow rate.

    Have you found the Squeeze’s flow rate to be easier/quicker enough to warrant the cost and weight penalty compared to the Mini?

  15. Great idea. Thank you for the terrific article.

  16. Great article, I found it after I began my similar project. Platy universal adapter cap substituted at clean end. Now I can fill collapsible Nalgene or Platy bags. Substitute dirty bag with a $1.97 5L water storage bag (bought two) fitted with blue cap. Total rig $40 without clean bag collection ( you probably have one). In line shut off valve not purchased yet. I want this to save water near camp without having to return to water source.

    • Get the hose crimp to shut off water flow within the inflow tube. It’s a very small piece of plastic and inexpensive. $12 gets you one and more spares than you are likely to need.

  17. wondering if anyone know if I can hack the platy Gravity system by using a mini-sawyer inline instead of the gravity works filter. I have had to buy two replacement filters already after just three backpacking trips of 4-5 days each. I tried backflowing maintenance and still they clog. I have had it! Cascade Designs has horrible customer service and won’t respond to my question as to why these filters have such a short life. Supposed to get a minimum of 25 cleans out of one filter. Thoughts?

    • Have you tried backflushing with a hot water/vinegar mix at home?

      What are the conditions of the water are you filtering? Is there much silt or mud in it? These types of filters do no deal well with very small particulates but the backflush method at home should restore it to normal function.

  18. It’s this stuff man. It’s just like…this stuff. More stuff. Ugg

  19. Nice. BTW, you can save the cost and complexity of the in-line adapter if you screw the filter directly on the bag and hang the long hose from the outlet. Gravity will pull rather than push the water through.

  20. Slightly off topic, but no matter what brand bag you use is it a pain to fill them from a shallow lake. Particularly if the bottom is muddy. I tried several things but the easiest way to fill a bladder bag is with a one gal zip freezer bag with about 1/4″ of one lower corner nipped off. You can scoop up a good quaintly of water in the freezer bag w/o stirring up mud. Then it is real easy to then fill your filter bag.

  21. Nice explanation with good photos – great job. The problem I have with this mod and with most I’ve seen is all that tubing. There’s just a lot of bulk there in addition to possible kinking and cuts. Here’s my solution using the Sawyer squeeze. I do everything Nathan shows to do to the “dirty” bag but I add a thin line from the s clip that makes the height of the bag adjustable from whatever you hang it from. Next I take two solid top lids found on 1 liter Smartwater bottles. After scuffing the tops of the lids with sandpaper I glue them together top to top, open ends facing away from each other, with JB Weld epoxy. Letting it cure overnight I then drill a largish hole through the lids from one threaded side to the other being careful not to damage the threads. Now I have a direct connector that will screw onto the clean side of the Sawyer Squeeze and onto an Evernew water bladder – the threads match so there’s no need for plumber’s tape – and it weights only 4 grams!. To use I fill the dirty bag with stream or lake water, attach the Sawyer Squeeze, attach my adapter to the outflow end and finally screw the Evernew bladder to the other end of the adapter. Hanging this entire setup to whatever, I use the line I’ve attached to the s clip to adjust it so the clean bag rests lightly on the ground taking some of the weight off the grommets in the dirty bag. So far this has worked every well for me and I can even use the adapter to back flush the filter. Comments welcome.

  22. Thanks! I’ve got some stuff and will throw this together and try it out. I’ll probably add a carbon inline filter too to add some chemical filtration. I appreciate the time taken for the writeup.

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