The Multipure Electronic Water Filter Capacity Monitor measures the number of gallons of water that flow through the filter and is used with the Multipure Undersink Water Filter with Arsenic Reduction (CBASSB). Increases filter capacity by almost 50% and will pay for itself in a few filter changes and indicates when to safely change your filter. Increases safe filter life to 1,000 gallons for CBASSB) Arsenic Undercounter units. Includes all necessary fittings and an electronic LED faucet ring indicator to take the guesswork out of filter cartridge replacement.