Black Packing Light
  • Sections
  • Today’s Features
  • Subscribe
  • Sign In
  • Subscribe
  • Home
  • Email Newsletter
  • Membership Info
  • Articles
    • Recent Features
    • Gear Reviews
    • State of the Market Reports
    • Gear Guides
    • Gear Lists
    • Skills & Techniques
    • MYOG
    • Science, Technology & Testing
    • Stories
    • Calendar
  • Education
    • Podcast
    • Webinars
    • Masterclasses
    • Online Courses
    • Guided Treks
    • Education Portal
  • Forums
    • Forum Index
    • Recent Forum Posts
    • Gear Forums
    • Gear Swap (Buy/Sell)
  • Gear Recommendations
  • Gear Deals

Backpacking Light

Pack less. Be more.

You are here: Home / New Features / Estimating the Age (Lifespan) of Your Backcountry Water Filter

Estimating the Age (Lifespan) of Your Backcountry Water Filter

by Jon Fong on August 16, 2019 New Features, Testing & Research, Wilderness Travel Skills

Background

I worked in the 3D printing industry for many years: actual jetting of material (not dispensing molten material through a single nozzle). We were using a 300 dot per inch printhead to generate solid objects and the printhead contained 1200 nozzles. Building a single 8” tall object was equivalent to printing 5000 pages.

Supplying the printhead with clean material was paramount to printing reliability as well as longevity. To assess this issue, a metric was developed to evaluate jetted material for cleanliness. This is called Conductivity Testing. To conduct the test, liquid was placed into the test apparatus and the fluid level was held at a constant level – this would provide a uniform fluid pressure. Downstream from the vessel was a standardized filter material. The liquid was allowed to flow through the filter and the data was collected. To generate a Conductivity Chart, you plot the real-time flowrate of the liquid through the filter material (Y-axis) against the total amount of fluid that had passed through the filter (X-axis). The chart would look like a straight line with a negative slope: high on the left side and diminishing on the right.

Conductivity

The slope of the line would give us the rate at which the filter clogged or in other words, a measure of the material cleanliness.  The minimum flowrate is defined by performance requirements needed to jet material correctly.  The total volume of material jetted is defined by marketing requirements. From this chart you can determine how many cubic feet (or pounds) of material could be jetted before the flowrate drops below acceptable levels.

Conductivity 2

The test metric is excellent for verifying material cleanliness, so we can apply this to estimate backcountry water filter performance.

However, we have no control over water quality in the backcountry. Modifying the test methodology to estimate effective filter area does add a lot more value to help characterize the performance state of the water filter.

It would be easy to replicate this type of test for water filters and the results would be highly repeatable. That being said, the system we used for evaluating 3D printing material quality, described above, is bulky and requires additional equipment that would make it difficult for most backpackers to emulate.

Thus, in this article, I am proposing a faster and easier-to-use test that, while not as accurate, the would be easy to replicate and is user friendly enough for most backpackers.

The goal of this test is to determine the effective age of your backpacking water filter based on comparing its current flowrate to its flowrate when new.

Procedure

I developed this test procedure using Sawyer Squeeze and Sawyer Mini filters, since they are probably the two most popular filter models in use by the lightweight backpacking and thru-hiking communities.

You can estimate the life of your Sawyer filter using a pretty simple test setup. The test requires that you measure the flowrate of a new filter in order to establish a baseline.

Darcy’s Law is used to characterize fluid flow through a filter media. However, this assumes that the fluid is free of particulates. By adding the assumption that the filter will become clogged over time, you can estimate the life of the filter by calculating the reduction in the effective filter area. By monitoring the flowrate, you can approximate the amount of useable filter (effective remaining filter area) that is remaining in your filter. Additionally, you can see the effect of backflushing on restoring the life of your filter.

Required Materials

  • Sawyer filter (or any other filter capable of operating in a gravity filtration mode)
  • 1-liter Smartwater bottle
  • digital scale

Instructions

Step 1: Drill a hole in the bottom of the Smartwater bottle. The hole should be small enough (~3/16” or 5 mm) that you finger can prevent air from leaking into the bottle. This is required to prevent a vacuum from forming in the water bottle during filtration, which will influence repeatability by altering the flow rate.

IMG 2988

IMG 2989

Step 2: Make sure that your filter is wetted out: I placed mine in a full glass of water overnight.

Step 3: Fill your sink (or a bucket of water) full of water.

Step 4: Submerge the bottle completely under water and remove all of the trapped air. Do the same with the filter and attach the two while keeping them underwater. In the picture below, the assembly is completely submerged below the surface of the water.

IMG 2986

Step 5: Place your finger over the hole on the bottom of the water bottle and raise the bottle/filter assembly out of the water. Water should not flow out of the filter (there may be a few residual drips, and that’s OK).

Step 6: Place a bowl on top of the scale and tare the scale.

Step 7: Suspend the bottle/filter over the bowl. Release your finger from the vent hole, and at the same time, start a stopwatch.

IMG 2985IMG 2987

Step 8: When the scale reads 500 grams (16.9 oz), record the time (in seconds) and end the test.

Test Results

For reference, I tested a brand-new (unused) Sawyer Squeeze filter and a used Sawyer Squeeze filter. The used filter has been my go-to filter for the last 5 years or so. I haven’t been judicious about backflushing or performing maintenance on the filter after my trips. I also do not have a clear idea as to how much water has been through the filter.

The test was conducted 3 times. Due to good repeatability, I elected not to include more replicate runs. The same batch of water was used for all tests and the water temperature remained constant. After the test, the filtered water was poured back into the main body of water.

The test was limited to 500 ml (16.9 oz) for 2 reasons. First, I was concerned about the impact of the reduced pressure head over time (h). As the water level dropped so would the flowrate and that could add error into the measurements. Secondly, my digital scale times out after 3 minutes so the change in volume (ΔV) had to be managed.

The following table summarizes my results with the new filter, the used filter, and the same used filter after a backflushing regime:

New Filter Used Filter Used, Backflushed
Time

(seconds)

57 103 99
56 105 97
57 100 98
Average 56.7 102.7 98.0

Theory of Operation & Data Analysis

Darcy’s Law was first used to describe fluid motion through permeable media (e.g., water flow through dirt and sand). Darcy’s Law has been used by engineers for decades to characterize filter performance. The basic equation is defined below:

K = ( ΔV * L ) / ( Δ t * A * h )

Where

  • K = hydraulic conductivity (volume/unit time)/filter surface area
  • ΔV = change in volume of water
  • Δt = change in time
  • L = specimen length
  • A = surface area of filter media
  • h = pressure head

Engineered filters are easier to analyze compared to earthen systems as a number of variables are under control.

K (hydraulic conductivity) is usually a design specification. A and L are defined by the physical design of the filter. For the purpose of this test, K, A, and L are all constants since we are comparing the performance of the same filters.

Darcy’s Law was formulated with the assumption that the fluid does not contain any contaminants (particulates). We can adjust the formula by assuming that as the filter clogs, the effective area of the filter is reduced.

Given the test protocol, the initial volume (V) is defined as a full bottle and the final volume occurs at the termination of the test when 500 ml (16.9 oz) has been filtered. Additionally, h (pressure head) is geometrically fixed as a function of the bottle’s dimensions.

Since K is a true constant between two filters having the same design, we can rewrite Darcy’s Law for both the new and used filter tests:

( V * L ) / ( tnew * Anew * h ) = K = ( V * L / tused * Aused * h )

V, K, L & h are basically constant over the course of any replicate tests so they cancel out of the equation.

The formula now reduces to:

1 / ( tnew * Anew ) = 1 / ( tused * Aused )

This can be rearranged into:

Aused / Anew =  tnew / tused

Thus, the ratio of the effective surface area of the used filter compared to the surface area of a new filter is proportional to the inverse of the time difference of the flowrates.

Data Analysis

Using my test data in the Darcy’s Law formula above, we can compare the performance of my used to a new filter:

  • In this case, 56.7/102.7 (tnew / tused) = 55%.  Assuming that Anew= 100%; Aused has 55% of the original effective filter area of Anew.
  • In my particular case, backflushing (3X) had very little impact on the flowrate (102.7 sec compared to 98.0 sec).

A Real World Model of Filter Degradation

Water quality is unknown and filtered volumes will vary.  Here is a graph speculating what can happen over the life of a filter.

Flowrate over volume

Each color represents a different backpacking trip. The decreasing slope of lines, e.g., may be a function of particulates clogging the water column (steep lines represent the filtration of water with higher particulate concentrations). The vertical spikes represent attempts to backflush the filter.

Commentary

Test Results

This simple test would provide insight about the effective surface area of your water filter’s media (in a sense, it represents a fuel gauge for the filter’s life).

No meaningful conclusion can be drawn from the backflushing results because the history of the used filter is not well-documented. More field data would be needed in order to clarify the effectiveness of backflushing, de-calcification, or any other mechanism by which filtration could be improved.

In an ideal world, one could measure results on (for example) 10 samples of new Sawyer filters to create a baseline range of flow rates for new filters. Users could then repeat the test protocol to estimate the actual effective filter area or life of their used system. If successful, the database could be expanded to include other gravity/squeeze-based filters.

Filter Type vs. Water Quality

Water quality around the country (world) is highly variable, so you must select the right filter for the right conditions. When camping in and around slot canyons and silty water sources, I usually bring my MSR MiniWorks filter because I can easily clean the filter element even in silt-laden water. Otherwise, I use the Sawyer Squeeze for 90% of my trips.

Sawyer Squeeze vs. Mini

When they first came out, the reported life of a Sawyer Squeeze was 1 million gallons (3.8 M liters) of water!

A million gallons is an absurd amount of water. I knew that the only way that they could claim those numbers were based upon something like continuous-flow (i.e., Conductivity) testing using some type of clean model water. Sawyer was forced to back off on those claims as they could not verify the claim with confidence, and it had almost zero real-world applicability.

The Sawyer Mini claims to have a filter life of up to 100,000 gallons (380,000 liters) of water. That’s great but the Mini has an order of magnitude less filter material that the Squeeze. After more than 5 years of use and abuse, the test results indicate that my original Sawyer Squeeze filter still has 55% of its life remaining. In terms of equivalence, that’s the same as about 5 Sawyer Mini filters!

In my opinion, the Sawyer Squeeze is superior with respect to flowrate, longevity and most importantly robustness (or latitude in its ability to resist clogging by problematic water sources). The biggest downside of the Squeeze for most people is the weight. That being said, the Sawyer Squeeze filter weighs only 1.0 oz (28.3 gm) more than the Sawyer Mini.

This test protocol proved to be very useful for me in making the decision to stick with the Sawyer Squeeze, for its performance-to-weight ratio vs. the Mini, especially with respect to its durability (longevity).

Related

  • Ryan’s Katadyn BeFree Filter Review
  • Andrew’s Sawyer Filter Review (Squeeze vs. Mini vs. Micro)
  • Josh’s Review of the Platypus GravityWorks Filter
  • A Survey of Water Treatment Methods (Article Series)

Disclosure: Some (but not all) of the links in this review may be “affiliate” links, which means if you click on a link to one of our affiliate partners (usually a retailer site), and subsequently make a purchase with that retailer, we receive a small commission. This helps us fund our editorial projects, podcasts, instructional webinars, and more, and we appreciate it a lot! Thank you for supporting Backpacking Light!

befree, gravity, katadyn, Sawyer, water filter, water filtration, water treatment

Get ultralight backpacking skills, gear info, philosophy, news, and more.


Comments

Home › Forums › Estimating the Age (Lifespan) of Your Backcountry Water Filter

Viewing 12 posts - 1 through 12 (of 12 total)
Forums are supported by our merchant partners (disclosure)
REI (Coupons) • ZPacks • Hyperlite • Patagonia • Arc'teryx • RBTR • Drop • Backcountry • Feathered Friends • CampSaver • Gaia • Mountain Hardwear
Gear Deals • Gear Search
Login to post (Basic Membership required)
  • Author
    Posts
  • Aug 16, 2019 at 1:52 am #3606296
    Jon Fong
    BPL Member

    @jonfong57

    Locale: www.flatcatgear.com

    Companion forum thread to: Estimating the Age (Lifespan) of Your Backcountry Water Filter

    The goal of this test is to determine the effective age of your backpacking water filter based on comparing its current flowrate to its flowrate when new.

    Aug 23, 2019 at 5:16 am #3607258
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    Hi Jon,

    Thanks for the detailed background and analysis. Would be great to gather more data across several filters and filter models, but that requires a lot of work.

    It seems like filters more-or-less gradually decline until (a) they stop working entirely or (b) I get too frustrated with the flow rate and decide to buy a new one. Generally, I try filtering some tap water just before each trip to make sure it still functions acceptably, and hope for the best. Maybe tracking flow rates with a repeatable scheme like yours would help me forecast that replacement date more accurately, and prevent backcountry surprises.

    — Rex

    Aug 23, 2019 at 2:55 pm #3607288
    Casey Bowden
    BPL Member

    @clbowden

    Locale: Berkeley Hills

    Jon,

    Great article. I don’t think I’m up to tracking the flow rates of my BeFree, but in the future I think I will:

    • Filter tap water just before the trip to make sure the filter still works OK (good idea Rex)
    • Bring a spare BeFree filter (it’s only 1.5 ounces)

    Casey

    Aug 23, 2019 at 7:04 pm #3607337
    Jon Fong
    BPL Member

    @jonfong

    Locale: FLAT CAT GEAR

    I believe that if this community got together to measure the performance of brand new water filters it would establish a good database.  Sawyer, BeFree, whatever.  I suspect the measurements of new filters will be very repeatable.  After that, everyone could get a sense of the remaining filter life of their respective filters.  At the heart of this is the UL concept of reducing redundancy via smart decision making.  With my 5 year old filter, I was flying blind until I got the data.  My 2 Cents

    Aug 24, 2019 at 6:30 am #3607392
    Terry Sparks
    BPL Member

    @firebug

    Locale: Santa Barbara County Coast

    <p style=”padding-left: 40px;”>I find it interesting that most backpackers will backlash their filters, which is what the manufacturer recommends and what I did for years.  While hiking thru the 700 miles of New Mexico on the CDT,  I started soaking the filter in warm water (110*-120*F)  for 20-30 minutes, shaking it out, then backflush for better results.</p>

    Aug 28, 2019 at 4:42 pm #3607939
    Jeff McWilliams
    BPL Member

    @jjmcwill

    Locale: Midwest

    I just got back from 2 weeks on the JMT and used a 2-year old Sawyer Squeeze.  For this trip, I switched from using the Evernew 2L bags to the CNOC Vecto 2L bags, because the Vecto bags have a clip that can be removed to completely open the back end of the water bag.  This makes it much simpler to fill the bag, particularly in standing water.

    However, I wasn’t very happy with the performance results.  When I would roll the CNOC bag like a toothpaste tube and put pressure on the bag, the flexible silicone like material would bulge rather than directly transfer all of my exerted force into water pressure.  The result was that I felt it took me longer to filter the same amount of water with the CNOC bags than it did using the Evernew bags.

    When I got home, I tried filtering clean water through the Squeeze using my Evernew bag, and was disappointed to see that the flow rate just wasn’t what I remembered it to be. While on the trail, I backflushed the filter 4 or 5 times using the included syringe, and I backflushed it again when I got home.

    I also flushed a diluted amount of CLR through the filter prior to our trip.  There’s a separate discussion about Sawyer and Katadyn BeFree flow rates, vinegar, CLR, and hardware scale deposits that can occur when sanitizing filters with bleach and hard water sources.

    On a whim, I decided to back flush my Sawyer again, this time using the blue female-female coupler sold by Sawyer, and by connecting the filter directly the faucet of my utility sink to achieve higher pressure.

    Back flushing at this higher pressure and volume appears to have made a marked improvement in performance.  Far greater than my best attempts at back flushing the filter with the syringe.

    Sadly, I did not measure before/after flow rates to quantify the change.

    I would encourage others with a Sawyer filter and the blue female/female coupler to try back flushing by attaching the filter to your utility sink faucet.   You may have to first unscrew the aerator from your faucet if your utility faucet has one.

    P.S.  The connection to the sawyer filter using the blue coupling connection wasn’t completely water tight.  Some water still sprayed out at the connection.  I just loosely wrapped my hand around the connection to prevent the leaking water from spraying up into the air and making a wet mess in my laundry area.

     

    Regards

    Jeff

     

    Aug 28, 2019 at 6:20 pm #3607957
    Arthur
    BPL Member

    @art-r

    Jeff  go outside and use a hose and let it leak!  I worry that the high pressure could have damaged the filter, thereby making flow faster by creating broken fibers and sideflows.  Is there any particle out there that is colored and the same size as a bacteria to use to see if it gets thru the filter as a test?

    Aug 28, 2019 at 6:28 pm #3607960
    Jeff McWilliams
    BPL Member

    @jjmcwill

    Locale: Midwest

    From https://www.sawyerdirect.net/FAQWaterProducts

    The fibers are very robust so please be FORCEFUL in your back flush process. When using the syringe do not be gentle, it will only form paths of least resistance instead blowing out the particulates that may be trapped in your filter. When using the faucet adapter, hold the adapter on the faucet and ‘turn the water up’ to ensure particle(s) removal.

    From https://www.sawyerdirect.net/sp174

    This Sawyer Faucet Adapter is for all Sawyer Water Filters and Purifiers. It connects the inline filter/purifier to most water taps. The adapter head is made of flexible PVC, which allows connecting to several different size faucet mounts. This faucet adapter is used for backwashing all Sawyer Filters and Purifiers, extending their life.

    The SP174 adapter is now very difficult to find, so I figured the coupling adapter was equivalent.

     

    Aug 28, 2019 at 6:34 pm #3607964
    James Marco
    BPL Member

    @jamesdmarco

    Locale: Finger Lakes

    I could suggest a slight improvement to the test apparatus to hold pressure (from gravity) constant as the bottle empties. Attaching the bottle to a longish spring (like a screen door spring) would raise the whole thing as the water flows out, but any improvement would be minor. You have a pretty solid testing apparatus.

    Oct 19, 2019 at 7:00 pm #3614700
    Jon Fong
    BPL Member

    @jonfong

    Locale: FLAT CAT GEAR

    I recently purchase a Sawyer Mini and conducted the same test.  The time to filter 500 ml was 150 sec so the approximated filter area is 56.7/150 or ~38% of the filter area of the Sawyer Squeeze.

    Saywer Squeeze ~ 3 oz (~$30)

    Sawyer Mini ~2 oz (~$20)

    The Sawyer Squeeze has about 3 times the filter area as a Mini and cost $10 more.  IMO, that’s money well spent.

    Jan 29, 2020 at 5:50 pm #3629254
    Jon Fong
    BPL Member

    @jonfong

    Locale: FLAT CAT GEAR

    I recently updated my filter flow test, instead of using a scale I used a graduated cylinder to measure fluid volume.  Additionally, I did some number crunching on the data and came up with some interesting results.  By using a new Sawyer Squeeze filter as a baseline, you can use the effective area of the filter (new=ideal) to make comparisons between new and used filters.  Additionally, when compared to a new Sawyer Mini filter, you can estimate potential performance.  In my analysis, I had three real data point: a new Sawyer Squeeze, a new Sawyer Mini and a 5-year-old Sawyer Squeeze.

     

    The Highlights are as follows;

    1. A new Sawyer Mini is over 2 times slower than a Squeeze
    2. After 5 years of use, my Sawyer Squeeze required about 50% more time to filter as a new Squeeze. The time to filter 500 ml went from 68 seconds to 103 seconds.
    3. If I had used the Sawyer Mini instead of teh Squeeze over those same 5 years, the flow rate would require 340% more time than a new Mini. The filtration time to filter 500 ml would have increase from 155 seconds to 680 seconds.  This seems to corelate to a lot of observations that the Mini clogs frequently.

    Here is the testing video

    Here is the number crunching video

    Jon

    Jan 30, 2020 at 8:18 am #3629308
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    the other thing about hollow tube filters like sawyer squeeze is don’t put bleach in it if you have hard water.  That will clog up the filter.  But you can use CLR/vinegar to clear it like Jeff said

    maybe the model of a filter gradually clogging up applies more to conventional filters like PUR or MSR?

    with a hollow tube filter like Sawyer Squeeze, if you backflush it clears most of the pores?  It would be interesting to test a new filter, then test it occasionally for a few years.  See if the flow rate gradually decreases.

    maybe sawyer squeeze lifetime is determined by one bad incident, like freezing it.

    does anyone have a Sawyer Squeeze they gave up on because it was too slow because it gradually clogged?  even though they used optimum backflushing as mentioned above – connect to faucet, use warm water/CLR/vinegar?

    I’ve used my Squeeze for 6 years and it works pretty much the same as new, although I haven’t measured it.

    Regarding freezing, if you shake all the water out of it then there’ll just be water in the hollow tubes, but they’re designed to expand when you backflush so they should withstand freezing

    Too bad there isn’t some solution that contains colored particles of some size greater than 0.1 micron.  If they get through the filter you could see it.

  • Author
    Posts
Viewing 12 posts - 1 through 12 (of 12 total)
  • You must be logged in to reply to this topic.
Log In

Want outdoor gear and skills info you can really trust?

Get our Handbook - the resource you need to make intelligent decisions about gear, safety, comfort, and pack weight.


Today's Gear Deals

Guide’s Gear Recommendations

Find out what gear our guides recommend if you want lightweight gear that is durable and versatile.

guide's gear logo

Gear Recommendations

  • Publisher’s Gear Guide
  • Staff Picks
  • Guide’s Gear Recommendations
  • Our Lightweight Gear Recommendations for REI Members
  • Today’s Gear Deals
  • Search for Gear on Sale

Subscribe Right Now

Receive new Members-only content, gain access to 2,000+ articles in the archives, and become a part of the most passionate community of backpacking experts in the world.
Subscribe Now
  • Backpacking Gear Reviews
  • Backpacking Skills
  • Backpacking Trips
  • Backpacking & Outdoor News
  • Outdoor Recreation Science & Technology
  • Backpacking Courses, Webinars & Other Events

Follow Us

Get outdoor skills and gear info you can trust.

Download the Backpacking Light Handbook to help you make intelligent decisions about gear, skills, ultralight philosophy, and reducing your pack weight.

Join Now: Support fair and objective product reviews.

Something for everyone: Basic, Premium, and Unlimited Membership options available.

View Subscription Options

More @ Backpacking Light

  • About Us
  • Jobs
  • Advertise with Us
  • Write for Us
  • Submit a Product for Review
  • Diversity Grants
  • Help / Support / Contact
  • Terms & Policies

Call Us

Membership Sales & Support: 406-640-HIKE (406-640-4453) | About

© Copyright 2001-2021 BEARTOOTH MEDIA GROUP, INC. | U.S. Library of Congress Serial Registration ISSN 1537-0364
BACKPACKING LIGHT® and the FEATHER/MOUNTAIN icon are registered trademarks granted for exclusive use to Beartooth Media Group, Inc. Subscribe here.

  • Subscribe
  • Log In
  • My Account
  • Forum Profile
  • Private Messages
  • Newsletters
  • My Course Enrollments
  • Unlimited Membership Portal
  • Help / Support / Contact