Phoenix Gravity New Millennium Edition™ filter cartridges and Black Berkey® cartridges are designed to remove heavy metals, but they do not remove mineral salts added by a water softener. Using softened water in systems equipped with Phoenix Gravity New Millennium Edition™ filter cartridges and/or Black Berkey® cartridges will prematurely clog the pores and reduce the filter’s absorption capacity. We therefore do not recommend using softened water with your Berkey® system and/or these filters. Using softened water in your Berkey® system (with any of these filter cartridges) will void the warranty.