Every 40 Gallons
Brita recommends changing the filter in its water pitchers after it has filtered about 40 gallons of water. The carbon and ion-exchange resin contained in the filter is effective in removing substances such as copper, chlorine and mercury from that amount of water.
Estimate how long your Brita filter should last. Divide 640, which is the number of cups in 40 gallons, by the average number of 8-oz. cups of filtered water your household uses per day. For example, a household that uses 7 cups of per day should change the filter every 91 days.
Change the filter on your Brita water pitcher after every 40 gallons to get the best results. For the average household, this will be approximately every two months.