Unscrew the aerator from faucet. If faucet threads are on the outside, attempt to attach the system directly to the faucet. If faucet threads are on the inside, select the proper adapter and washer provided and attach to the faucet. Support the base and insert the water filter until it clicks. Turn on the faucet to flush the new filter for 5 minutes. The 100 gallon filter life begins after this. Replace filter after approximately 100 gallons or about every 4 months. Substances reduced may not be in all users' water. Brita Faucet Water Filter Systems fit standard faucets only. They do not fit pull-out or spray style faucets.