What filter ensures the best purification?

ENG
 
 

This question is important for anyone who decided to choose a filter for home use. Indeed, to what extent do the advertising promises to remove all contaminations from tap water deserve trust? We asked this question to a specialist knowing the actual situation, head of the Group of Environmental Microbiology of the Pasteur Research Institute, Doctor of Medical Sciences Vladimir Malyshev.



Geyser:  Mr. Malyshev, have you indeed performed tests that “unmasked” the existing filters?


V.M.: It was interesting to us to compare such popular water treatment systems as stationary three-step treatment filters. These filters are installed under the wash-bowl, and purified water is fed from a separate tap. Because of high popularity of such filters, it was important to understand how efficiently they perform as barriers against microbiological contaminations.
 


Geyser: Have you checked the filters for all contaminations?


V.M.: It is impossible to check the reliability of filters with respect to removal of all kinds of viruses and bacteria that can occur in water. After analysis of a large number of water supply systems with bacterial and viral contaminations, we chose the two most important lines of tests: first, with human rotavirus, and second, with Escherichia coli.

 


Geyser: What are the results of the first test?


V.M.: We took three models of stationary filters of popular brands, widely available in shops, namely, Geyser filter and filters from two other producers. We tried to provide in a laboratory the conditions under which the filter operates at home. For this purpose we took common tap water in which viruses were initially absent (i.e., after sterilization), after which the viruses were introduced, and 1000 l of water was passed through the filter.

 

The data obtained show that only the Geyser filter has reliable barrier properties, with no rotaviruses detected after it. Filters of other producers partially transmitted rotaviruses or showed no barrier function at all.


 

Geyser: What are the results of the test with Escherichia coli?


V.M.: This test is particularly important for household use of a filter. A filter can accumulate bacteria like a sponge and then discharge them to the purified water. Therefore, we contaminated the filters with Escherichia coli and again passed water through them. We performed tests with three concentrations of Escherichia coli: 3.5×102, 2.0×104, and 2.2×105 colony-forming units per milliliter.



Geyser:  To what do these concentrations correspond?


V.M.: Such concentrations are possible only at emergency discharges of contaminants into water-supply systems. Actually the first two levels are possible in open water basins, and the third level is typical of wastewaters.



Geyser:  How successfully did the filters operate?


V.M.: Only with the Geyser filter Escherichia coli was absent, and reproduction of bacteria in all the concentrations was suppressed. The other filters showed considerably worse results. One of them was efficient only for the lowest concentration, with significant breakthrough at higher concentrations. The other filter did not appreciably retain Escherichia coli at all. 



Geyser:  What conclusion can be made from the results of these tests?


V.M.: Among the three stationary filters tested, only the Geyser filter operates efficiently and ensures barrier function against viral and bacterial contamination of water after 1-month experiment (approximately 6 months of real operation). This is apparently due to the fact that Geyser filter treats water with Aragon material. Its complex structure is impermeable to rotaviruses, and silver present in this material suppresses reproduction of bacteria.





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