A Survey of Water Hazards and Water Treatment Methods - Part 5: Filtration Methods

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We will try to break them all down into a few categories, but there are several 'dimensions' to this. First, how is the water pushed through the barrier? We have the following methods: all create pressure:

Pump
Gravity
Straw

Because any type of barrier can become blocked by all sorts of stuff in the water, almost every larger filter offers some sort of replaceable 'cartridge'. What sort of barrier is in the cartridge - again, there is a range:

Conventional
Hollow fibre
Other

Clearly, these terms are going to need some explanation. By conventional we mean something vaguely resembling a cylinder where the outer surface is the actual barrier or membrane. These cylinders may be ceramic, fibreglass, or similar. Hollow fibre technology is fairly new and is based on technology developed for kidney dialysis. The 'other' category covers various unreliable techniques and one reliable one based on ion-exchange resins. We will go into greater detail shortly.

One could almost have a third dimension for 'filter life', but this is complicated by what kind of water is used. Most filters last a reasonable length of time if you only use really sparkling clear water in them, but things change when the water has suspended matter. Some filters still last a long time; others block up very quickly. I don't have a laboratory to examine this reliably, so I have used water from the dam on my farm for simple comparisons. No, this water is not 'sparkling clear, and many creeks are better than this, but this sort of water is representative of actual conditions. The photo here shows me testing the MSR Hyperflow pump for a previous review.

ARTICLE OUTLINE

Introduction
- Straws - Two cautions
Conventional, Pump
Hollow Fibre Filters, Pump and Gravity
- Getting the pressure
- Sawyer - Filters for Bacteria and Protozoa
- Sawyer Purifiers
MSR
Platypus
LifeStraw
Other Filters
- General Ecology
- Pure Hydration
Summary

# WORDS: 4350
# PHOTOS: 13

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This topic has 33 replies, 22 voices, and was last updated 8 years, 1 month ago by Geoff Caplan.

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Aug 21, 2012 at 4:28 pm #1293210

Stephanie Jordan
Spectator

@maia
Locale: Rocky Mountains

Companion forum thread to:

A Survey of Water Hazards and Water Treatment Methods – Part 5: Filtration Methods

Aug 25, 2012 at 1:49 pm #1906009

Jerry Adams
BPL Member

@retiredjerry
Locale: Oregon and Washington

Because it's freezing before and after when I'm sleeping so I'de have to carry it in my pocket.

Aug 25, 2012 at 1:55 pm #1906011

Cayenne Redmonk
BPL Member

@redmonk
Locale: Greater California Ecosystem

Too bad there isn't some way to test a filter after it's been frozen a bunch of times.

How much would you pay to have your filter tested and certified ?

Aug 25, 2012 at 2:00 pm #1906016

Jerry Adams
BPL Member

@retiredjerry
Locale: Oregon and Washington

"How much would you pay to have your filter tested and certified ?"

I would like Sawyer to test their filter (after freezing) and report the results : )

Aug 26, 2012 at 10:37 pm #1906340

T N
BPL Member

@tordnado
Locale: Europe

Thanks for the comment. According to themselves they DO remove chemicals. I have been in contact with them and both their webpage and their E-mail answers claim that they do. I have requested a test report.

If bwtechnologies actually remove chemicals I will choose it before the Saywer filter however if they cant back up their claims the Saywer stays on top!

Sep 6, 2012 at 9:18 am #1909624

T N
BPL Member

@tordnado
Locale: Europe

I have benen trying to get an answer from http://www.bwtechnologies.com for quite some time now! The first replies where prompt and good but when I asked about a test report they have not gotten back to me at all! Suspious!

Sep 11, 2012 at 11:31 am #1911308

Hikin’ Jim
BPL Member

@hikin_jim
Locale: Orange County, CA, USA

It seems like the one really serious drawback to filtration is that there's no way to verify that it's working (short of having access to a very sophisticated laboratory).

With boiling, I can feel the heat and see the bubbles. With a Steripen, I can observe the light. With chemicals, I can taste and smell the chemicals. There's no way of knowing if a filter is working. What if I got the "lemon" out of that last production batch?

Is anyone aware of any studies that might give us an idea of how many failures per "X" number of filters manufactured there are?

Is there any way to garner an idea of how effective filters really are?

HJ
Adventures in Stoving

Mar 17, 2013 at 12:21 pm #1966695

Jim Milstein
Spectator

@jimsubzero
Locale: New Uraniborg CO

I made a female/female adapter by hot-gluing two bottle caps together then drilling a hole through the unit. I also made a narrow-mouth adapter for the Nalgene wide-mouth Cantene, which fills much easier than a narrow-mouth bottle or bladder.

So, if you squeeze dirty water from the Cantene through the filter into another bladder, connected with a F/F adapter, you are set up for a back-flush by simply inverting the arrangement and squeezing a bit of the clean water back through the filter then discarding the wash water from the dirty water bladder. Though it is unnecessary to do this often, it is trivially easy to do.

Mar 17, 2013 at 12:34 pm #1966698

Ken Thompson
BPL Member

@here
Locale: Right there

If you don't want to make your own. Look at these.

http://jetflow.com/product-detail/?pid=247

Oct 21, 2016 at 6:52 pm #3432269

Geoff Caplan
BPL Member

@geoffcaplan
Locale: Lake District, Cumbria

I’ve used the Seychelle bottle filter for some years now (marketed in the UK as the TravelTap). It’s affordable and lightweight, giving around 1600 litres per filter. Water flow reduces towards the end of its life so you’ll know when it need replacing.

It’s a zero faff system with good flow and no need for pumping, squeezing or backflushing. I simply fill up the filter bottle and any other containers at the source, and decant from the dirty containers to the filter container as I go. There’s an inline version as well for bladder users.

Performance has been validated by a number of NGO tests and Government labs including the US Red Cross and the UK military.

I’ve had a couple of chats with the UK distributor DrinkSafe, who have detailed knowledge of the comprehensive Ministry of Defence testing (they’re a great company to deal with, by the way). Although many backpackers are concerned about the performance of filters with viral pathogens, the Seychelle posted very good results. While viruses are in theory smaller than the micron rating of the filter, it seems that in practice they are normally attached to larger particles which are filtered, so only minimal concentrations get through. The distributor also deals with Sawyer, and in his view the better portable filters should all be effective with viruses – it’s just that most of them haven’t been tested. It’s surprisingly difficult to find authoritative information on this issue, so I thought I’d pass this on for what it’s worth. Caveat emptor..

I put the Seychelle to quite a stern test when I was given duff information and was caught without water in an arid Karst area. I was reduced to drinking from a blood-warm pool contaminated with cow-dung. No ill effects, though I now carry some tabs for additional peace of mind in extreme circumstances. I also do a lot of walking on Dartmoor which has fecal contamination from livestock and have never been infected.

Overall, I’m finding it a pretty good solution.
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