The ability of water filter elements to remove harmful bacteria from a water source is directly related to the ‘pore size’ of the material through which the water flows. Sizes for the most common disease-causing bacteria; anthrax, botulinum, e.coli, listeria, streptococci and staphylococci range between 0.5-1.0 microns across. Hence, a filter element that is expected to largely eliminate these harmful bacteria should have a pore size between 0.1 and 0.2 microns.
Note that viruses are far smaller than bacteria (some as small as 0.07 microns across), and cannot be removed by most common water filters. However, small amounts of diluted bleach kill bacteria, viruses and parasites. Consequently, a good water treatment plan should include both the filtering of water as well as a purification step such as boiling or treatment with bleach.
If a water source happens to be from an agricultural and/or industrial area then the water may also contain dangerous heavy metals, many of which can be removed by filter elements that incorporate activated charcoal. Distillation is another means or removing heavy metals from water, although this method requires time and energy that may be in short supply during a disaster. A good alternative to distillation is to collect rain water. Even rain water, however, should be purified before being considered for human consumption.
Our book, “When There is No FEMA – Survival for Normal People in (Very) Abnormal Times” provides a wealth of information on the proper collection and treatment of water in survival situations.
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