How Effective are Backflushing and Storage Practices for Squeeze Filters

[Billy (2 Bees) Bowers]

Ryan, great article. I picked up my first Sawyer because it removed the most bacteria even though it has a low flow rate like my old school First Need. Been an outdoorsman for 50 plus years and was fortunate not to get sick taking water from streams filtering through cloth only till 30 years ago when I was taking water, I noticed a herd of mountain goats up stream. Be one with nature, but come home healthy and safe.

[Daryl and Daryl]

Thanks for doing the hard work for us.  Very helpful.

[Luke R]

<p style=”text-align: right;”>I noticed that deionized water (DI water) was mentioned here a couple times for the final flush. I am curious about this as I have hard water in our tap at home and wasn’t sure if I could just buy purified or distilled water at the grocery store to use instead. Are those hard waters? Where do I get DI water, or how do I treat water I have to make it this way? I’m not a chemist of any sort, so this is a little beyond me. Thanks!</p>

[Jerry Adams]

distilled water would work.  It has very little minerals in it that could clog a filter

[Fred Kelly]

Question for Ryan – I would love for you/Ryan to comment on what your “standard” (default/starting) process is/would be for cleaning a filter prior to storage after normal use (say a filter that hadn’t materially clogged yet).   If you aren’t doing the cleaning/disinfection process in attempt to standardize/compare filter performance, but say your main goal was just to be proactive prior to filter layup/storage (to optimize flow rate and filter life), would you always use the Citric Acid as a step prior to disinfection?  (or would you only use the weak acid/solvent if/when flow rate falls of)?   Would you incorporate a warm water “soak” at the start of your “standard” layup process to dislodge material?   After storage, would you incorporate a warm water “soak” when taking a filter from storage, prior to use?  Thoughts on using the Chlorine Dioxide vs the Bleach?

Thanks for takin time to do all the testing/research!

This is a really great article from ~5 months ago in Nov 2021 – just what I needed!  This type of deep dive adds value – thanks!  I learned a ton from this article, and your/Ryan’s rigor, (and some follow up with Sawyer/Katadyne printed and support info).   I learned several concepts that weren’t previously clear to me (even though I thought I had read all the instruction manuals for Sawyer/Katadyne – not!).    In your testing, you came up with a good/standard process where the filter flow rates/results could logically be compared after using them.  Your process had steps I hadn’t thought of (had missed previously).  I’m leveraging this work, and the follow up deep dive I did into all three filter manuf’s printed cleaning/storage info, as well as some info from Sawyer’s Customer Svc group responding to my Q’s.     My goal is to incorporate all these concepts optimally as I return from trips, and/or prior to heading out with a filter that has been stored (BeFree or a Sawyer Squeeze).   One of my hiking partners has the QuickDraw.

I’m like many of you – I have used the Sawyer Squeeze since 2013 (~9 years), a year after they came out in 2012 (I have qty 2 of the Squeeze filters still going strong), and in 2020, after watching a million video’s and reading articles on the BeFree, I made that jump (I bought qty 3 prior to a 200 mile AT section hike in Virginia, and have only needed to use one of those qty 3 BeFree’s since then – haven’t needed to use the other two yet).  I have put ~ 350 liters thru that first BeFree without any plugging or material flow rate reduction (AT & Colorado 14er climb), but hearing other’s issues, I have either carried…, or included a  spare BeFree in resupply boxes on long section hikes (which haven’t been needed, yet).

The big picture fundamental concepts (which this article brought into focus) which I didn’t have “organized” logically in my mind include

1. Backflushing – OK – all of us have known how important that is was, but I hadn’t ever thought of doing that to a BeFree using a smartwater bottle with the sports cap.  I didn’t have it clear how similar in technology, all three brands were.

2. Use of warm water.   I see Sawyer strongly recommends starting with a warm water soak when we are attempting to maintain/restore flow (loosen crud up), and…, to get a filter back in service after it has been stored.   Makes sense that the warm water might be able to loosen up crud.

3. I had never heard of the use of weak acid wash to dissolve solids/calcium/deposits (you/Ryan used Citric Acid which I now see is a great low cost safe weak acid – used for a million things including canning – which can be a solvent for the deposits in the filter).   I also now see that Sawyer similarly recommends soaking a filter in white vinegar (and then backflushing) if  the warm water soaking & back-flushing don’t restore flow rate.    I’m betting this is a technique/step that many other people are also unaware of.   It makes sense.   If  solids/calcium/deposits have accumulated in the filter, and back-flushing doesn’t dislodge them, and the filter dries (allowing those deposits to harden/solidify/clog the filter), I now understand how this step possibly helps to dissolve/dislodge those solids/calcium/deposits (with the weak acid solvent) where they can be flushed out (going fwd, or possible backwards via back-flushing).      I’m wondering/betting that many abandoned filters could have possibly been restored via the use of warm water soaking, and/or…, use of an appropriate slightly acidic solvent (Citric Acid, White Vinegar, etc).

4. Ryan’s work helped me see that either Chlorine Dioxide (Micropur or Aquamira) or bleach is used/recommended to disinfect.   All three of the filter manuf’s list/show bleach as OK.   Katadyne lists bleach or Chlorine Dioxide.   Also, Ryan’s work (and other comments I now understood), helped me understand the potential negatives of leaving the Chlorine in the filter.

 

Here is the procedure used in Ryan’s “standardized” test (to insure comparable results):

a.       Filters were backflushed at a high squeeze pressure with 2 liters of cold tap water.

b.       Filters were forward-flushed with 0.25 liters of a 5% citric acid solution and rested for 30 minutes, then flushed with 0.5 liters of cold water. This treatment removes calcified organic deposits such as magnesium and calcium salts that may form when filtering hard waters normally found in the Mountain West.  (Note inserted:   in some other BPL blogs, although not blessed by BPL, user(s) have used vinegar/acetic acid Ph ~2.4 and CLR/ lactic acid, gluconic acid are acids while the CLR’s Ph ~3.7) to dissolve deposits in backpacking water filters).

c.       Filters were forward flushed with 0.25 liters of a double-concentrated solution of Aquamira (Chlorine Dioxide), rested for two to four hours, and then flushed with 0.5 liters of cold water. This treatment is designed to disinfect bacterial biofilms which may foul the filter membranes. The cold water flushing after the Aquamira (Chlorine Dioxide) is designed to remove traces of chlorine-based oxidizers which are known to accelerate aging of polymeric filter media.

 

Parallel (very similiar to Ryan’s standardized test procedure for cleaning filters), what follows is a great email response from Sawyer’s Cust Svc folks when I contacted them asking some Q’s:

“……For general maintenance, we recommend backwashing your filter after each outing, when your flow rate begins to diminish, before prolonged storage, and when you’re ready to start using your filter again.  Backwashing your filter after storage is a great way to re-wet the filters and restore the flow rate before use.

Soak the filter in hot water (not to exceed 135 F) for ~30 min to loosen up any residual particulate built up in the filter fibers and then backflush several times with hot water as hard as possible.  If the flow is slow, repeat the process for a blocked filter below.

A blocked filter can almost always be recovered by soaking the filter in hot water (not to exceed 135 F) for an hour or so, and then backflushing several times with hot water as hard as possible.  The trick to a successful backwashing is to be very forceful with the process. Water will always take the path of least resistance, so in order to fully flush out the filter and restore its flow rate, make sure you are exerting as much pressure as you can, especially during the first couple of passes.

If that doesn’t work and your flow rate is still slow, your water source might be mineral rich, so we would suggest soaking it in plain, undiluted white vinegar for an hour or more, and then repeating the process with hot water backflushes in order to dissolve the minerals that have hardened on to your filter.  A second or third soak of hot water and/or vinegar may be necessary. The more you do this, the more recovery you will achieve.

To sanitize the filter, we’d recommend using a weak bleach solution (one capful of bleach per Liter of water).  Slosh the weak bleach solution around in your pouch and run it through the filter.  After the pouch and filter have been sanitized, let the filter sit upright with sufficient ventilation to dry out before storing the filter in a cool/dry location away from direct sun exposure.  Some tips:

Trying to filter water through a blocked filter will always make things worse.
Backflush, backflush, backflush,……

When storing, make sure to finish with the sanitization process above.

Our backwashing tips and tricks video can be seen here:

https://sawyer.com/videos/backwashing-tips-tricks/

 

Hope that helps!…”.

Question for Ryan – I would love for you/Ryan to comment on what your “standard” (default/starting) process is/would be for cleaning a filter prior to storage after normal use (say a filter that hadn’t materially clogged yet).   If you aren’t doing the cleaning/disinfection process in attempt to standardize/compare filter performance, but say your main goal was just to be proactive prior to filter layup/storage (to optimize flow rate and filter life), would you always use the Citric Acid as a step prior to disinfection?  (or would you only use the weak acid/solvent if/when flow rate falls of)?   Would you incorporate a warm water “soak” at the start of your “standard” layup process to dislodge material?   After storage, would you incorporate a warm water “soak” when taking a filter from storage, prior to use?  Thoughts on using the Chlorine Dioxide vs the Bleach?

Thanks Ryan et all!

[Scott S]

Hi, Ryan. I may be a little dense but I still can’t figure out how to backflush the BeFree based on your answer above. Could you (or anyone else) please add a picture or two to show what you’re doing, including the donut gasket?

[tkkn c]

I use a Sawyer coupling to back flush.  It fits the Sawyer filters, it is very tight on the befree.  I do not have a leak at the junctions, so the coupling is doing it job.   Attached are a few pictures of the backflush setup.

[Alan W]

I have used a garden hose end gripped together with the BeFree to provide very strong flushing and great recovery once at home. Be careful with max flow and pressure though, for 1 out of my 4 blew apart.

Alas, I’ve stopped buying BeFree due to short life in field.  I could not obtain life of > about 5 days or 80 miles on mountain streams in CO & NM at summer consumption rate.  Would end up using chemical backup before end of trip or resupply.

I loved the high initial flow and simplicity but hated the poor endurance and ineffective swishing (ha!!) backflush.

Might reconsider with Sawyer coupling and spout removal.

[Arthur]

Alan, I have the same experience in CO and Wyoming.  Few days and the BeFree is dead using what looks like extremely clear water.  What is your alternative filter?

[JCH]

I don’t do any overnight backpacking in the summer months…just too darn hot, sweaty and tick/mosquito infested down here, so my filter sits unused for 6 months. Previously I had pretty much accepted that I might need to buy a new Squeeze filter each Fall.  I am currently conducting an experiment where, after a thorough end-of-season flush which included a few drops of bleach in distilled water, I am storing it over the summer completely full of distilled water (I fashioned a water-tight plug for the input side of the Squeeze).  I will report back in November :)

[Alan W]

Arthur, I used Sawyer on AT; but I switched to HydroBlu Versa 4-5 years ago. Vs. Sawyer, it has noticeably faster flow, lasts longer between backflushes, is easier to backflush (threads both ends), has integrated watertight caps both ends; but specs have 1 less 9 in removal rating, last I checked.

[JCH]

Interesting…both Sawyer and Hydroblu claim a 0.1 micron pore size but Sawyer claims five 9s for bacteria:

Rated to 0.1 micron absolute filtration, the Squeeze Filter removes 99.99999% of bacteria such as salmonella, cholera, leptospirosis, and e. Coli, and removes 99. 9999% of  protozoa such as giardia and cryptosporidium (independent testing laboratory Hydration, LLC.; microbiological report S05-03). The Squeeze Filter also filters out 100% of microplastics.

vs

The Versa Flow removes 99.9999% of all bacteria, such as E.coli, salmonella, and cholera. It also removes 99.9999% of all protozoan cysts, including giardia and cryptosporidium

I wonder if there is anything in Sawyers claim of  “0.1 micron absolute” pore size that accounts for this difference?

Also, regarding filter longevity and the ability to effectively backflush, Hydroblu explicitly states that they orient the fibers to filter from the outside in.  Wondering if Sawyer filters from the inside out?

[Roger Caffin]

Hydroblu explicitly states that they orient the fibers to filter from the outside in.
I think that is normal. When you backflush, the pressure is on the inside, so the soft plastic tubes expand ever so slightly, loosening the trapped bugs and wogs. So the theory goes, anyhow.

It sticks in my memory that the difference between 7x 9s for bacteria and 6x 9s for the much larger protozoa may really be an artifact of the test method. To count bacteria you put the water in a culture so the bacteria grow and become more visible, which makes them easy to count. But counting protozoa is more difficult as they do not get larger and so are harder to see.

Cheers

[JCH]

When you backflush, the pressure is on the inside, so the soft plastic tubes expand ever so slightly, loosening the trapped bugs and wogs. So the theory goes, anyhow.

Hmmmm.  So if the tubes expand, then it stands to reason the pores also expand…ever so slightly.  If so, the tubes then need to be very good at returning to their original size to avoid degradation of effectiveness.

[Jerry Adams]

Squeeze disassembled.  You can see the hollow tubes – there are many of them, quite small diameter

When you backflush, you put pressure on the inside of the tubes so they expand, along with the pores so they’re slightly bigger to release any particles.

They test this so I think the tubes and pores keep working for a long time.  They advertise a large number of cycles.

A couple other pictures:

 

 

[Jerry Adams]

[Roger Caffin]

the tubes then need to be very good at returning to their original size to avoid degradation of effectiveness.
They are. One of the ‘wonders’ of polymer chemistry.

Cheers

[Terran Terran]

A drop of Dawn. Rinsed well.

[David D]

I baby my filter but am seeing something strange.

Immediately on returning from every trip, I backflush with ~ 5L tap water.  This gets rid of any sediment on the inlet which then is nice and white and clean looking.

I follow that up with a mild bleach solution to sterilize it following Platys recommendation.  No distilled water follow up.

It then gets left in front of a fan for for a week on high speed and next to a dehumidifier 24/7.  Based on weight, it dries pretty quickly.

After about 3 or 4 days in front of the fan, I see this.  When it’s primed for next trip, it’s white again.

Anyone know what is happening here?   I’ve seen this exact same behaviour with 2 different quickdraws now.

Wouldn’t it be unlikely to be a biofilm because its disinfected immediately and dried quickly?  I also backflush in the field often and never let it sit unused and wet for longer than 24 hours

[Bill in Roswell]

Mineral deposits most likely. A vinegar soak will eliminate most. The Platy and BeFree and similar filters have a limited lifespan of 1000 liters  for a reason. No amount of cleaning can overcome that.

[Bill Budney]

I wouldn’t suspect biofilm after the bleach and flush. However, I wouldn’t be surprised if sodium/calcium hypochlorite dry to sodium/calcium chloride — salt.

I’ll bet that Platypus support has seen this question before.

(EDIT: Or, yeah, as the other Bill says, other minerals from your tap water.)

[David D]

I was thinking salt/deposit as well, thanks for the feedback.  I’ll reach out to Platy and share if they have anything new to say.  I’ve done the vinegar soak in the past, agree it can help.

[Bill Budney]

It is interesting that Platypus skips the distilled water rinse (after bleach) that some other instruction include. I wonder why they skip it, and whether it would leave you with a clean-looking filter?

[David D]

Platy Gravityworks recommend 2 drops bleach/L.  Platy Quickdraw recommended 1/4 ts per L in ’22 but it was a typo (2.5ml<> 1/4tsp) which they corrected to 1/2 tsp in ’23.  MSR (owned by the same company as Platy, Cascade Designs) Trailshot (which I also own) recommends 1/4 tsp bleach per L (but again, with the same typo, 2.5ml<>1/4 tsp) but then a final “clean water” rinse, not even distilled.

3 filters, 3 different storage recommendations, same company.

I’ve used a final distilled water rinse in the past to reduce the chance of bleach blocking the filter but I believe it leaves the opportunity to go foul if not 100% dry.  Depending on Cascade’s feedback, I may go back to a final distilled rinse and just make sure its ultra dried.

I hold extra backup filters at home just in case, and carry purification tabs as back up on trips.

[Bill Budney]

Yep (on all points).

I suspect the reason for such wide variation in bleach amounts (2 drops to 2.5ml) is because bleach evaporates after opening, so you never know the real concentration of home bleach. Maybe two drops of fresh bleach is enough, but 2.5ml should work even if your bleach is ancient.

Shame that you have to stock backup filters, but that’s the current state of the art: None of them last forever.

[Author]

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