This year, I used my Sawyer Mini while hiking the Arizona Trail (AZT) and the northern California section of the PCT. Before both hikes, I flushed the filter with vinegar to dissolve any hard-water mineral deposits. Prior to every back-flush on trail, I knocked the filter against a hard surface (a tree-trunk or the edge of the sole of my boot) for 30 seconds. After each hike, I performed the knock-on-wood treatment until back-flushes stopped producing debris. Then I measured the filter’s flow-rate before proceeding with hot-water treatment. In my previous filter-related post, I didn’t describe hot-water treatment in detail.
Hot water (HW) treatment
Here’s what I used.
- Sawyer Mini filter and syringe
- Pyrex bowl
- Microwave oven
- Digital food thermometer
Per Sawyer’s directions, do not heat the water above 140℉. Your timing and power levels will differ from mine, so be careful.
- Back-flush the filter and put it in the bowl.
- Fill the bowl with enough water to cover the filter.
- Microwave the bowl at maximum power until it reaches 140℉ (about 3 minutes).
- Microwave the bowl at 10% power for 20 minutes. The water will cool by a few degrees.
- Back-flush the filter with a syringe full of <140℉ water.
- Put the filter back in the bowl and top it up with cold water.
- Microwave the bowl at maximum power until it reaches 140℉ (about 20 seconds).
- Repeat steps 4 thru 7 until the total step 4 soak-time is six hours.
- Back-flush the filter with cold water three times.
The table for the Sawyer Mini is the one of interest. It shows how long the filter took (min:sec) to fill a 24 oz. (0.71 liter) bottle. The corresponding flow-rates are also shown, and abbreviations are as follows.
- VG = Vinegar
- HW = Hot water
- KW = Knock on wood
- HW+KW = After each 20 minute soak (HW step 4), the filter got 30 seconds of knock-on-wood
- Rows 1&5 – the flow-rate reduced by 3.2 oz/min on the SoCal PCT.
- Rows 5&7 – the flow-rate reduced by 8.2 oz/min on the AZT.
- Rows 4&5 – knock-on-wood treatment loosened some debris that hot water didn’t.
- Rows 6 & 7 – hot water treatment loosened some debris that knock-on-wood didn’t.
- Rows 7&9 – hot water treatment combined with knock-on-wood is more effective than hot water alone.
Knocking the Sawyer Mini against a hard surface for 30 seconds prior to every back-flush on trail definitely improved its flow. The filter is still clogged during this year’s hikes, but more slowly than in 2021, when I wasn’t constantly knocking the crap out of it. As a result, the knock-on-wood treatment after this year’s hikes produced less debris compared to the same treatment post-PCT last year.
In my previous Sawyer-related post, I guessed that knock-on-wood treatment provided all the benefits, and more, of hot water treatment. I was wrong. I still think hot water treatment is too time-consuming to be practical during a thru-hike. However, it does loosen some debris that knock-on-wood doesn’t. Combining hot water with knock-on-wood is the most effective treatment.
I’m skeptical of any claim that a filter is good for 100,000 gallons. Unsurprisingly, how long it actually lasts will depend on the quality of the water being filtered. Hiking the AZT caused a much greater drop in flow than hiking the same distance of the southern California PCT. So, how long will this filter last?
- Distance so far: 2500 miles
- Typical daily hike: 20 miles
- Maximum daily amount filtered: 2 gallons
Using these numbers, I estimate that I’ve filtered a maximum of 250 gallons using my Sawyer Mini. During that time, its flow-rate has dropped from 0.25 gal/min to 0.188 gal/min. Assuming the filter degrades linearly, the chart below shows it losing about 10% of its flow every 100 gallons. Back-flush efficiency might improve slightly as the flow-rate drops, which would slow filter degradation. On the other hand, I drink less than two gallons per day on trail, so this projection is a best-case scenario.
The filter will be completely clogged after 1000 gallons, but it’ll be unbearably slow before then. I think my frustration threshold is about 0.1 gal/min, after 600 gallons, when the filter is at 40% of its original flow. (The Vecto started leaking after approximately 300 gallons.)
I’ll try the following.
- Flushing the filter with carbonated water.
- Gravity filtering. I estimate that the pressure inside a Vecto might be as high as one pound per square inch when I’m squeezing it hard. If I reduce the pressure, debris is less likely to get permanently stuck in the filter.
I’ll be more skeptical about filter longevity claims.
- Maybe a specification looks too good to be true.
- A specification might be misleading when it says “up to” instead of “at least”.
- Perhaps a spec is deliberately vague. After all, there’s a lot of variation in the quality of water sources and the pressure that people apply when filtering.
Specs should be specific
So here’s my attempt at writing one.
The Sawyer Mini flow-rate will be at least 0.1 gallons per minute after filtering 600 gallons at a maximum inlet water pressure of 1 psi
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