A water filter is a device that removes pollutants from water to make it purer. This is a generic term for a variety of devices and techniques, most commonly used to filter tap water for domestic use. A water purifier is designed to purify water in the same way as a water filter, the difference being its ability to remove specific elements that a simple water filter cannot.
Water filter, water purifier, what is the difference?
In addition to a variety of pollutants that are removed by a water filter and that depend on its design, a water filter must be able to remove bacteria as well as protozoa. Protozoa are small, often solitary organisms present in water, some of which are parasites, responsible for malaria or certain dysentery for example.
A purifier, on the other hand, has the ability, in addition to bacteria and protozoa, to remove viruses.
But to be classified as a water purifier, a device must not just filter out viruses or bacteria, but must do so at a specific removal rate. For bacteria, Klebsiella Terrigena was chosen as the control population. This bacterium is often found in unpolluted soil or in surface or drinking water. The viruses are a rotavirus (responsible for gastroenteritis) and the polio virus. The elimination rate for bacteria must be greater than 99.9999% (log-6) and greater than 99.99% (log-4) for viruses.
The concept of "log" is used to qualify the level of filtration. "log-2" means a filtration level between 0 and 99%. "log-3" means a filtration level between 0 and 99.9%. "log-4" means a filtration level between 0 and 99.99%, and so on. In other words, if the filtration level of bacteria is at log-3, it means that a system with this fineness allows 10 times more bacteria to pass than a system calibrated at log-4.
The Berkey® systems were evaluated on this basis and the results can be seen in the following table.
Standard removal rate (norm)
Berkey® removal rate
|Bacteria||> 99.9999% (log-6)||99.9999999% (log-9)|
|Virus||> 99.99% (log-4)||99.99% (log-4)|
The Black Berkey® filter elements used in all systems meet or exceed the standard for water purifiers. In addition, the bacterial removal of the Berkey® systems is 1000 times higher than that recommended by the standard.