How to Evaluate Water Filter Specs

January 11, 2014

in Water

Water is an essential for survival. We can only last a few days without water. The standard rule is three days, but the last day often involves enough physical and mental impairment, that replacement water needs to be procured within two days or we face a severe threat of death from dehydration. Water is not always hard to find, but water that we can drink without consequences may be. This makes a good water filter or other means of purifying water one of our most valuable survival tools.

Water filter manufacturers like to sell their products by displaying their strengths, not their weaknesses. We need to know how to evaluate the specs we see in order to make a good purchasing decision. Here is a list of specs and evaluation guidelines:

  • Type of filter – most filters involve some kind of particle filtering but not all do and many filters combine several different techniques of filtering water.
    • Pre-filters – simply remove large particles and some sediment to prevent the fine filter from getting quickly clogged. If our filter doesn’t have a pre-filter, it’s not difficult to use a piece of cloth or screen to perform this function or even just allow water to settle sedimentation to the bottom before putting the cleaner top portion of the water through our filter.
    • Particle filters – hollow fiber membrane, glass fiber or microporous ceramic filters; all work by allowing only very small particles and clean water to pass through them.
    • Chemical filters – activated carbon and other supplementary components can remove chemicals from water that particle filters are unable to remove. These components usually can not be renewed and must be replaced when they lose effectiveness.
  • Particle size filtered – for the particle filter component of our filter, we generally want the filter to be able to remove particles at least down to the one micron size. Here is a list of particle sizes that are often found on water filters:
    • 1 micron – filters out some bacteria, some large chemicals, and most but not all dusts, insecticides, paints and more. This level does not remove some dangerous bacteria or viruses.
    • 0.1 micron – filters out all bacteria, most but not all large chemicals, paints, insecticides and more. This level does not remove viruses.
    • 0.01 micron – filters out most but not all viruses, dusts, large chemical molecules, proteins and toxins. The viruses we are mostly concerned about for human health are removed at this level. Note that even at this level, some chemicals and toxins may be passed through the filter. This is why some filters also use components designed to remove chemicals.
  • Lifetime volume – the volume of water that a filter can process and still be effective varies tremendously. Some filters can be “back-flushed” to extend their effective life, while others simply lose effectiveness and need to be replaced.
  • Flow rate – with most filters this is not very important, but it may be worthwhile to pay attention to how fast the filter can pass water.
  • Price – “straw-sized” filters can start at around $10. Portable filters usually run in a range from $20 – $200 but vary substantially by how many components (pre-filter, filter, chemical filter, pump) are used. Household filters can produce more drinking water, often use several of the same type of component (like multiple ceramic candles) and cost in the hundreds of dollars, depending on configuration and performance.

Here are some of the best filter lines to consider:
Most Sawyer filters are hollow fiber membrane, with particle sizes of 0.1 microns (filters bacteria) and 0.02 microns (filters viruses). They come in a “mini” size for $20 rated for 10,000 gallons and normal sized for $40 rated for 1,000,000 gallons. They can be ordered with a variety of flexible bags, bottles and fittings and can be backflushed to extend lifetime.

Katadyn concentrates on camping/backpacking portable filters and offers a wide range of options from ultralights designed for one person to a gravity drip canister with three ceramic filter elements. Most use some form of ceramic filter element but often combined with other elements. The lifetime, flow rate and price vary with the individual filter configuration.

Makes a single person “straw” filter and a family sized filter. The LifeStraw Family 1.0 combines a pre-filter, a 2 liter feed bucket, a 0.2 hollow fiber membrane filter to eliminate all bacteria, and a mechanism for backflushing to extend lifetime to around 5,000 gallons. For $75, this is a very easy to setup and use filter with clear/graphic instructions on a plastic container designed to keep the filter unit sanitary until it is needed for use.

It’s important to understand how we intend to use the water filter. For just a simple filter with no extras, buckets or pumps, Sawyer is hard to beat on the specs of either 0.1 or 0.02 micron filters, very high lifetime numbers and good prices. But if we need a portable filter for camping and backpacking that’s easy to use and contains a hand pump to force water through the filter, Katadyn sets the standards that other companies have to live up to. LifeStraw filters don’t measure up to the standards of other filters on specs alone, but are probably the most simple to use, specially for a beginner. And they donate some of the proceeds from the sales of their filters to provide school children in Africa with clean drinking water. For household needs, the larger ceramic candle based filter units like Berkey or AquaRain are excellent products.

JUMPSTART: Water1 – Overview
Sawyer Inline Water Filter

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