What is the Micron Rating of the Black Berkey® purification elements?

With respect to the micron rating, we do 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 ...