Regarding the micron index, nmcl does not use or publish a micron index for the Black Berkey® elements for the following reasons:
There is a lot of confusion with regard to the nominal and absolute in microns ratings. An absolute note in microns is that which indicates the maximum size of the pores expected in an element. The nominal microns note is the average size of pores in the element. This means that if 90% of the pores are 0.02 micron and 10% of 2 microns, one could claim that the nominal rating of the micron is 0.2 micron, which would imply that the bacteria and pathogenic parasites would be completely eliminated . But in reality, most of the water would go through the wider pores of 2 microns and thus allow bacteria and parasites to pass through. Consequently, an allegation of nominal value in microns can be very misleading.
Regarding the absolute rating in microns, there are also confusion because there are two different standards to determine the absolute; In the United States, the standard is 99.9 % of elimination, but the international standard is 99.99 % elimination or 10 times more elimination.
Intelligent marketing specialists can use confusion on the above differences to reveal the product "A" as being better than the "B" product while product B can be much higher. For example, we used to report an absolute note using the international standard because we have a large international clientele. Several years ago, we published a note on our ceramic filters. A particular company began to publish that our elements were 0.9 micron while theirs were 0.2 micron. However, our microns note was based on an absolute (international) value while theirs was based on nominal value ( US) assessment. During tests at Spectrum Labs, it was found that in the range from 0.2 to 0.3 microns, our filter eliminated more particles than the other brand. Unfortunately, many people make their purchasing decisions based on a microns rating which can be legitimately distorted and to a large extent.
Based on the above information, we decided not to participate in the publication of a note in the micron. Rather, we think that an absolute rate of elimination of pathogenic bacteria is a much better measure because it is much more difficult to abuse it. Based on this criterion, the Black Berkey® purification elements eliminate 99.9999 % of pathogenic bacteria such as E.coli. To our knowledge, no other personal filtration element can match this capacity.