Depending on how much you use your cartridge-type water filter, replace its cartridge one to two times a year. When you replace the cartridge, also thoroughly clean the canister that houses the cartridge. Also clean and lubricate the o-ring with food-grade silicone grease or a comparable lubricant.
Dispose of your self-contained water filter (a filter without a removable cartridge) when it reaches the end of its useful life. This type of filter usually lasts from 6 months to 1 year.