As the most popular Berkey system—mostly due to the fact that it's a perfect size for 2-4 people—the Big Berkey Water Filter is constructed of highly polished 304 stainless steel and comes with two Black Berkey purification elements (expandable to four), plus two chambers, two blocking plugs, a lid, spigot, and a rubber gasket base. Up to four PF-2 Fluoride and Arsenic filters can be installed into the lower chamber.