With respect to the micron rating, NMCL does not use or publish a micron rating for the Black Berkey® elements for the following reasons:
There is much confusion with respect to nominal and absolute micron ratings. An absolute micron rating is one that states the maximum pore size expected within an element. The nominal micron rating is the average pore size within the element. This means that if 90% of the pores are .02 microns and ten percent are 2 microns, one could claim the nominal micron rating as .2 microns, which would imply that pathogenic bacteria and parasites would be totally removed. But in reality the bulk of the water would channel through the larger 2-micron pores and thereby allow both bacteria and parasites to pass through. Therefore a nominal micron-rating claim can be very misleading.
With respect to the absolute micron rating, there is also confusion because there are two different standards to determine absolute; in the US the standard is 99.9% removal, but the international standard in 99.99% removal or 10 times greater removal.
Clever marketers of products can use the confusion over the above differences to make product “A” appear to be better than product “B” when product B may be far superior in reality. For example, we used to report an absolute rating using the international standard because we have a large international customer base. Several years ago we published a rating on our ceramic filters. A particular company began to publish that our elements were .9 microns whereas theirs were .2 microns. However, our micron rating was based on absolute (international) while theirs was based on a nominal (US) rating. When tested at Spectrum Labs, it was found that at the .2 to .3 microns range our filter removed more particulate than the other brand. Unfortunately many people make their purchasing decisions based on a micron rating that can be legitimately distorted and to a significant degree.
Based on the information above, we decided not to participate any longer in publishing a micron rating. Rather, we think an absolute pathogenic bacteria removal rate is a far better gauge because it is far more difficult to abuse. Based on that criterion, the Black Berkey® Purification Elements remove 99.9999% of pathogenic bacteria such as E.Coli. To our knowledge, no other personal filtration element can match that capability.