Black Berkey Purification Elements are more powerful than any other gravity filter element currently available. The micro-pores within the cleanable Black Berkey purification elements are so small that pathogenic bacteria are simply not able to pass through them. Berkey PF-2™ reduction elements are designed for use in conjunction with Black Berkey™ water purification elements to adsorb the following unwanted elements found in drinking water. Fluoride, Arsenic V, and pre-oxidized Arsenic III