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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