Pur RF3375 2 Stage Faucet Mount Filter 1Pack For use with all Pur faucetfiltering systems this replacement cartridge provides healthy greattasting water right from the tap in two stages. First it reduces sediment making it cleaner. Second it reduces lead and 99.97percent of the microbiological cysts cryptosporidium and giardia while leaving beneficial fluoride in the water. For best results the filter should be changed every 100 gallons approximately two to three months. A builtin Automatic Safety Monitor gauge indicates how much filter life is left and automatically shows when it should be replaced.