Regarding micron rating, NMCL does not use or publish a micron rating for Black Berkey® elements for the following reasons:
There is a lot of confusion regarding nominal and absolute micron ratings. An absolute micron rating is one that indicates the maximum pore size expected in an item. The micron rating is the average pore size in the element. This means that if 90% of the pores are 0.02 microns and 10% are 2 microns, one could argue that the nominal micron rating is 0.2 microns, which would imply that disease-causing bacteria and parasites would be completely eliminated. But in reality, most of the water would pass through the larger 2 micron pores and thus allow bacteria and parasites to pass through. Therefore, a micron rating claim can be very misleading.
When it comes to the absolute micron rating, there is also confusion because there are two different standards for determining the absolute; in the United States the standard is 99.9% removal, but the international standard is 99.99% removal or 10 times more removal.
Clever marketers can use confusion over the differences above to make product "A" appear to be better than product "B" when product B may actually be much superior. 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 note on our ceramic filters. One company in particular started posting that our elements were 0.9 microns while theirs were 0.2 microns. However, our micron rating was based on an absolute (international) rating while theirs was based on a nominal ( US) rating. In testing at Spectrum Labs, it was found that in the 0.2 to 0.3 micron range, our filter removed more particles than the other brand. Unfortunately, many people make purchasing decisions based on a micron rating which can be legitimately misrepresented to a large extent.
Based on the information above, we have decided to no longer participate in publishing a micron rating. Rather, we believe that an absolute rate of elimination of pathogenic bacteria is a much better measure because it is much more difficult to overuse. Based on this criterion, Black Berkey® purification elements eliminate 99.9999% of pathogenic bacteria such as E.Coli. To our knowledge, no other personal filtration item can match this capability.
