imperial berkey gravity-fed water filter with 2 black berkey elements and 2 berkey pf-2 fluoride and arsenic reduction elements berkey equipped with powerful black berkey elements, the 4.5-gallon imperial berkey water filter system sits on a countertop or stand, and addresses over 200+typical contaminants that could be present in tap water and raw, freshwater sources like rivers and ponds. the imperial berkey water filter system is portable and effortless to use—no tools, electricity, or plumbing are required. just pour untreated water into the top chamber and dispense clean, refreshing water from the spigot. the system is constructed of highly polished aisi 304 stainless steel. we recommend replacing black berkey elements after 6,000 gallons, depending on the quality of influent water. each additional pair of black berkey elements (sold separately) adds an additional 6,000 gallons of typical contaminant reduction to your system before replacement is recommended. berkey pf-2 fluoride and arsenic reduction elements adsorb fluoride, arsenic(v) and pre-oxidized arsenic(iii), and other residual typical heavy metal ions. we recommend that each pair of berkey pf-2 fluoride and arsenic reduction elements should be replaced after 1,000 gallons of use, under normal conditions. black berkey elements and berkey pf-2 fluoride and arsenic reduction elements are backed by independent, third-party testing.