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 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.
This is a proprietary type of carbon block filter that claims to have a higher sediment-holding capacity than other carbon block filters.
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.
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.
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.
These systems use ultraviolet light to kill bacteria and other microorganisms. They cannot remove chemical contaminants.
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.
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%
- .01 micron is 10 nanometer
- .02 micron is 20 nanometer
- .025 micron 25 nanometer
- 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
- The Company’s product information website: http://sawyer.com/products/sawyer-complete-4-liter-dual-bag-water-purifier-system/
- Filters .02 micron
- 1 million gallon
- Removes 99.997% of Viruses, 99.99999% Bacteria, and 99.9999% Protozoa/Cysts
- Berkey Water Filtration System
- The company’s specifications are available here: http://www.berkeyfilters.com/berkey-answers/performance/filtration-specifications/
- N/A because it is a purifier not a filter.
- 3,000 gal per element (multi-element capable systems)
- Viruses: 99.999% reduction, Pathogenic Bacteria Surrogate: >99.9999%, etc .. see link
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.