I bought a Sawyer inline water purifier about a month ago, hoping it would replace my General Ecology First Need water filter which is about 12 ounces heavier. Both the Sawyer and the First Need are the only EPA approved filters on the market capable of filtering giardia, cryptosporidium, and viruses. The Sawyer (model sp125) weighs 2.9 oz. dry and 6.7 oz. when saturated with water. It has an maximum life time of 3000 gallons with regular back flushing and is designed to be compatible with gravity feed bags and hydrations systems. The Sawyer uses a fast flow hollow fiber membrane to filter water. When water is drawn though the membrane, it flows through the sidewalls of fibrous tubes that have holes in them and trap any organisms or impurities greater than 2 microns in size.
I field tested the Sawyer with two different hydration systems using Platypus bladders and MSR Nalgene Wide-mouth Canteens. Unfortunately, the Sawyer did not perform well in either configuration, and I’ve concluded that you can’t suck on a hose hard enough to draw water through a 2 micron filter. You need a pump. Period.
In my first field test, I connected the Sawyer filter about 6 inches from a 96 oz. Nalgene bladder which I filled with unpurified water. In this configuration, dirty water flows from the bladder through the inline filter where is it purified. From there, the clean water travels through about 2 feet of plastic tubing to a hydration system bite valve. Both the filter and the bladder are stored in the backpack and the hose is threaded through the backpack’s hydration port. In this configuration, I was able to suck some water through the system but only enough to wet my mouth, not slack my thirst. With each draw on the hose, I also swallowed a lot of air and the entire system was marginal. Gravity filtration in this configuration was also very poor and it took about 10 minutes to filter 2 cups of water. That really sucked because I had to do it at night on top of a cold mountain.
In my second field test, I connected the Sawyer filter about 12 inches from a 3L Platypus bladder and attached the inline purifier outside of the backpack onto a shoulder strap of my pack to test the effect of having a very short tube between the clean end of the filter and my mouth. I tried this variation because I thought that placing the suction closer to the filter might improve the flow of water through it.
I filled a 3L platypus bladder with water in my kitchen and attached the Sawyer to the shoulder strap of my pack. It was a little awkward but not bad. I sucked on the tube at home and the flow was much better, so I packed up the car and drove to my local testing ground for a 9 mile hike. About a half mile into the hike, I took a sip and nothing happened. I couldn’t pull any water through the filter. I stripped off the pack and checked to see if I had any kinks in the hose. Nope. So I removed the entire system from my pack and held the bladder over my head to check if I could at least get a gravity feed to work. Nothing again. I checked the filter lock, and that wasn’t an issue either. So I broke down the entire system, removed the Sawyer, threw it in a mesh pocket, and continued my hike. When I got home, the Sawyer filter went into my big box of unloved, rejected hiking toys.
My conclusion after trying these two different hose configurations is that you need the pressure that can be generated by a pump-action system to push the water through a 2 micron filter if there is any distance between the water source and the bite valve. This is the reason why a filter like the Aquamira Frontier Pro, despite its ecological deficiencies and 3 micron pore size, works with a soda bottle reservoir. But if you use an inline filter with a hose-based hydration system and refuse to change, I’m convinced that you are SOL and need to stick with pump filters given the current state of the art in inline water purification.
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2 users commented in " Sawyer Inline Water Filter and Purifier - Field Tests "
Follow-up comment rss or Leave a TrackbackI don’t think the in-line filter is getting a fair shake here. For an in-line, gravity-fed filter to work there must be a column of water above the filter because it is this height that actually provides the force to push the water through the filter. The technique relies on a simple equation from physics and static fluids, p = p0+d*g*L where the pressure at the filter is p, p0 is the pressure at the top of the water column, g is gravity and d is the density of water. The difference in pressure is what produces the force to push the water into the filter. So you can’t have your hose loop around, it must be straight down and they aren’t made for sucking through.
The suggestion of using a pump type filter is irrelevant because as I see it you are trying to make a system that will work while moving but with a pump you will have to stop and manually pump so why not just use a gravity filter like it is intended, hung from a tree or you can even hold it up yourself, if you are going to stop anyways. A pump filter actually runs a little slower than a gravity one, hand pump filters are usually 0.5-1.0 L/min while a gravity filter can filter 1+ L/min. I suspect your tree system was so slow because you didn’t have an air hole in your reservoir. Think about a can of soda, if you turn it upside down it’s very difficult for the liquid to flow out smoothly because it is creating a vacuum behind the fluid, but if you puncture the other side of the can it can “breath.” Every time you got a burst of air in your system it was because the reservoir was trying to equalize the pressure in the bag. Providing an air hole will probably solve the problem but it may still be too difficult to suck through.
I’d agree with you if the Sawyer were marketed as just a gravity filter, but it’s not. It’s intended to be used as an inline filter in a bite and suck hoser system, and for that it fails miserably.
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