Unscrew the aerator from faucet. If faucet threads are on the outside, attempt to attach the system directly to the faucet. If your faucet has threads on the inside, you will need to use one of the adapters provided. Attach base system to your faucet and then insert filter cartridge into filter cup. Flush the new filter cartridge with cold water for 5 minutes. The 100 gallon filter life begins after the 5-minute conditioning period.