Understanding Water Filtration, by Old Soldier

The understanding of water filtration requires a look at various filtration methods as well as contaminants. Let’s take a look at these.

Water Filtration Methods

Carbon/Activated Carbon Filters

Activated carbon chemically bonds with and removes some contaminants in water filtered through it. Carbon filters vary greatly in effectiveness. Some just remove chlorine and improve taste and odor, while others remove a wide range of contaminants, including asbestos, lead, mercury, and volatile organic compounds (VOCs). However, activated carbon cannot effectively remove common “inorganic” pollutants, such as arsenic, fluoride, hexavalent chromium, nitrate, and perchlorate. Generally, carbon filters come in two forms– carbon block and granulated activated carbon.

Carbon block filters contain pulverized activated carbon that is shaped into blocks under high pressure. They are typically more effective than granulated activated carbon filters, because they have more surface area. Their effectiveness depends in part on how quickly water flows through.

Granulated activated carbon filters contain fine grains of activated carbon. They are typically less effective than carbon block filters because they have a smaller surface area of activated carbon. Their effectiveness also depends on how quickly water flows through.

Ceramic Filters

Ceramic filters have very small holes throughout the material. These holes allow water through but block solid contaminants, such as cysts and sediments. They do not remove chemical contaminants.


These filters use an ion exchange process that removes mineral salts and other electrically charged molecules (ions) from water. The process cannot remove non-ionic contaminants (including trihalomethanes and other common volatile organic compounds) or microorganisms.


This technology heats water enough to vaporize it and then condenses the steam back into water. The process removes minerals, many bacteria and viruses, and chemicals that have a higher boiling point than water. It cannot remove chlorine, trihalomethanes or volatile organic chemicals (VOCs). Distillation is good for removing nitrates, which can be a problem in high water table or farming areas.

Fibredyne Block

This is a proprietary type of carbon block filter that claims to have a higher sediment-holding capacity than other carbon block filters.

Ion Exchange

This technology passes water over a resin that replaces undesirable ions with others that are more desirable. One common application is water softening, which replaces calcium and magnesium with sodium. The resin must be periodically “recharged” with replacement ions.

Mechanical Filters

Like ceramic filters, these filters are riddled with small holes that remove contaminants, such as cysts and sediments. They are often used in conjunction with other kinds of technologies, but sometimes are used alone. They also cannot remove chemical contaminants.


Ozone kills bacteria and other microorganisms and is often used in conjunction with other filtering technologies. It is not effective in removing chemical contaminants.

Reverse Osmosis

This process pushes water through a semi-permeable membrane that blocks particles larger than water molecules. Reverse osmosis can remove many contaminants not removed by activated carbon, including arsenic, fluoride, hexavalent chromium, nitrates, and perchlorate. However, reverse osmosis does not remove chlorine, trihalomethanes, or volatile organic chemicals (VOCs). Many reverse osmosis systems include an activated carbon component than can remove these other contaminants. Quality can vary tremendously in both the membrane system and the carbon filter typically used with it. Consumers should also be aware that reverse osmosis filters use 3-20 times more water than they produce. Because they waste quite a bit of water, they are best used for drinking and cooking water only.

UV (ultraviolet)

These systems use ultraviolet light to kill bacteria and other microorganisms. They cannot remove chemical contaminants.

Water Softeners

These devices typically use an ion exchange process to lower levels of calcium and magnesium (which can build up in plumbing and fixtures) as well as barium and certain forms of radium. They also do not remove most other contaminants. Since water softeners usually replace calcium and magnesium with sodium, treated water typically has high sodium content. Some people may be advised by their physicians to avoid softened water. For the same reason, it is also not recommended for watering plants and gardens.


The list of contaminants was too long to include, so I am just referencing it.


The smallest contaminants are viruses, such as the:

The smallest known virus to man is the DNA virus Porcine circovirus type 1. It has a genome of only 1759 nucleotides. Its capsid diameter is only 17 nm.

Log Levels

Using base 10 system to depict the decreased contamination level that can be easily converted to percent reduction. Log of 1 is 10, log of 2 is 100, and log of 3 is 1000. Perhaps the easiest way is to think of the log value being the number of zeros past the real number value.

In percentage form, it looks like this:

1-log reduction = 90%
2-log reduction = 99% Ecoli
3-log reduction = 99.9% Cryptosporidium
4-log reduction = 99.99%
5-log reduction = 99.999% Giardia
6-log reduction = 99.9999%
7-log reduction = 99.99999%

More Information



  • .01 micron is 10 nanometer
  • .02 micron is 20 nanometer
  • .025 micron 25 nanometer
  • etc.

Recommended Products

  • Lifesaver Filter
    • The company website: http://www.lifesaverusa.com/
    • Filters to .015 micron 15 nanometers
    • 6000 liters
    • Removes Bacteria, Viruses, Cysts, Parasites, Fungi Log 7 or 99.99999%
  • Sawyer Purifier System
  • Berkey Water Filtration System


    I did not include popular filters like the Katadyn because my research showed that most of them (including the Katadyn) did not measure up well to the filters listed above. It’s hard to tell at first, but when you do the nanometer/micron conversion it becomes clearer. Katadyn pocket for instance measures its filtration in .2 micron. Compare that to the filters above. .2 microns is 200 nanometers as compared to the lifesaver at .015 micron and 15 nanometers. That means the lifesaver filters 13.33 times more efficiently than the Katadyn.


  1. Great info, thank you.
    Water is by FAR the most important prep, it cannot be talked up enough. So many preppers don’t realise the importance of readily available clean water.
    For those of you on public water systems, you have some work to do.

  2. Some time back I was conned into buying a fairly expensive water distillation setup from a fellow who frequents the ‘Survival’ online community. His overstated claim was that it’s the very best and only method of reliable water purification. He failed to mention as you point out, about the relative boiling points of contaminants, OR another glaring shortcoming – the immense amount of energy need to make the conversion from water to steam back to water. Thanks for drawing attention to the boiling points! And thanks for taking the time to write up this useful information.

  3. I’ve been reading countless hours on water filtration etc. however I haven’t seen much in the way of combinations, like in any grid down scenario what would be the optimal setup to and end of the purest water possible? Using a number of methods in a particular order such as Charcoal-iodine-distillation-reverse osmosis-reminearlization/alkalization?

  4. Great article! good side-by-side comparisons of the various systems out there. Important to note that no one system is going to remove everything, but will greatly reduce concentrations enough to have minimal effect. As an engineer, I personally like reverse osmosis with carbon pre-filters for drinking/cooking water. Good systems can be bought at big box building supply stores (or online) for around
    $150, and can be installed under a kitchen sink by the average homeowner. These systems are only as good as long as you have pressured water system. In a grid down situation, with no water pressure, other gravity systems would have to be used. Please make note that all systems using some sort of block or membrane filtering media are subject to damage if they freeze, and may become ineffective.
    Also note that while distillation will not generally remove chlorine and VOCs just running a straight distillation, those chemicals can mostly be removed by discarding the first portion of the distillation (say the first 1/4), and saving the last portion. Since the chlorine and VOCs usually come off the distillation first, you capture and discard them in that first portion. (which is why bootleggers and distillers dump the first 1/4 (the “Heads”) of their distilling runs, and only keep the ‘Middlings’ or middle 1/2 of the run. Makes for a cleaner product).

    1. I’ve never made any “shine”, so I have zero knowledge, but my mind telling me that the first but of moonshine is good for sterilizing instruments. I’m going to have to look this up because it can’t be right.

  5. Good article. One advantage of living in the upper Midwest is most houses have a basement with a sump. Mine is ALWAYS filling with water. So in a grid down situation I merely fill my Big Berkey and filter it. Since this is groundwater it is fairly pure already, easily good enough to wash in.

  6. EV,
    What you are looking for is too dependent on the water in your area. You would need a water test and then research filters based on what you need to remove.

    You are correct, many filters are sensitive to freezing including all block and ceramic filters and I believe the LifeSaver is as well.
    I didn’t know about the details of distillation and VOCs. Good to know!

    I just moved and on one of the tasks this summer is to break out the 5 year old LifeSaver and see how it is. I do seem to remember its shelf life going down after use. Meaning it can be stored and then used but used and then stored wasn’t so good for it.

  7. I’m not an engineer, but have done a fair amount of research. Since a grid failure induced by EMP/CME could last for decades, it occurred to me that alternative energy is going to be as critical as water purification. The two, in my mind, are inter-linked, since gravity-operated systems and most/all “emergency” filters will clog much earlier than expected when used with ditch water instead of tap water. Ratings on these are based on tap water. I went with the Lakewater Filter, manufactured in Michigan. It is designed to process water from streams and lakes or ponds. Uses three sediment filter jars, 20 micron, 5 micron, and .35 micron- to capture sediment, bacteria, cysts, protozoa, copepods, an in-line chlorinator (uses calcium hypochlorite), a large carbon filter to capture a long list of chemicals, and UV sterilizer (55 watts) to nail any life forms that might sneak through the gauntlet. You can search it on line using Lakewater Filter, Equinox. I’ve used one on my stream in rural Utah with good effect. Spare sediment filters are affordable, and the UV bulbs last a year in continuous service. I operate my UV sterilizer only when processing a batch to fill my 500 gallon holding tank, then shut it down. I have four spare bulbs and lots of filters. The carbon unit lasts for 700,000 gallons. State lab tests reveal zero chloroforms and the test for nitrates came back .001 parts per billion. Testing is pricey, so I limited my lab testing to what I thought were the greatest problems in my area. Portable filters have their place for mobile use, but seriously, are you going to provide enough water for showering, dish washing, toilet flushing with a Berky? Pathogens can infect you from BOTH ends….so using ditch water for toilets has its perils. Going to wash your clothes with ditch water? Yuk!
    So get serious about alternative power, and alternative water filtration. A national recovery will take much longer than you think!


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