The Pentek S1 is a 2-1/2" x 9-3/4" cartridge that is meant for general water filtration purposes. These cartridges are economically priced and are highly effective at reducing sediment particles down to 20 microns. The Pentek S1 is recommended to be used only for chlorinated water supplies and should not in well water applications where there is no chemical injection system. Purchase Pentek water filters from Serv-A-Pure today. Shop now!