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Platypus Pre-Filter Cap for Sawyer 3 Way SP122 Water Filter

Aaron Zagrodnick



Back in Issue 3 we Reviewed the Sawyer SP122 3 Way Water Filter and since that time I’ve used the filter on several additional trips. It’s still working quite well provided that clean water sources are selected and the water is pre-filtered before using it inline or while in gravity mode.

Platypus Pre-Filter Cap for Sawyer 3 Way SP122 Water Filter

During the review, we tested the SP122 against 100 liters of average mountain stream water (With no pre-filtration) that dramatically reduced the flow rate of the filter. With Sawyer’s 1 Million Gallon Guarantee, we thought that following the backflushing instructions would at least get us pretty close to the original flow rate after filtering only 100 liters of water, but unfortunately this wasn't the case. Even after hours of backflushing, (The instructions call for 30 seconds) we were only able to restore the flow to about half of what we got with the filter when new in a gravity test. (Check out the review for the full breakdown of the test and filter specifications) The results were a bit disappointing - however considering how well the filter worked when new, its .1 micron rating, and its small size / light weight I picked up a new filter and decided that I’d be adamant about using some type of pre-filtration at all times to extend the filter’s life.

In the field, I fill up a Platypus Hoser 3L hydration reservoir with dirty water which then quick-connects to the Sawyer Filter to form an inline hydration system that can also be hung to work in a gravity configuration. Wanting a really light and simple method of pre-filtering the water, I at first simply used the mesh out of a tea strainer cut to size and inserted into the inside of the cap from an older Platypus Hoser Hydration system that was past its prime. This cap already has a large opening perfect for the purpose, but a similar setup could also be made by drilling out a normal Platypus Cap / replacement cap. At a water source, I remove the Platypus from my pack, screw on the cap with the filter mesh in place, and then proceed to fill up my water supply by scooping / pouring dirty water over the mesh and into the Platy.

Original Cap with Larger Mesh
The original cap above worked well, but wasn't perfect.

Cut into a circle, the mesh fits nicely into the inside of the cap and stays in place on its own. It’s a simple and clean solution, but in practice I found that the mesh I was using was still letting too much debris into my dirty reservoir. Additionally, the friction fit inside the cap isn't a perfect fit, so larger debris would still find a way to sneak around the edges, into the Platypus, and subsequently into the Sawyer Filter I was trying to protect in the first place. Hoping to resolve the issue, I picked up a Medelco #4 Cone Permanent Coffee Filter for just a couple bucks. The mesh on this filter is really fine, and so far, has been doing a great job of pre-filtering.

New Cap With Coffee Filter Mesh

The new mesh isn't quite as springy as the larger diameter mesh previously used, so the inside the cap friction fit doesn't work quite as well and I wanted to attach the mesh to the outside of the cap this time just to prevent anything from sneaking through. After hacking the mesh out of the filter frame, I attached the mesh to the outside of the cap using an 8” cable tie, being careful to tuck the rough edges of the cut mesh back up and under the tie itself before fully securing the tie tightly. The result is a .15 ounce solution, and while it isn't quite as pretty as the original cap, it’s much more effective and should work to keep the Sawyer going!

Ziptie Construction




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