The life of your refrigerator water filter is dependent upon the volume of contaminants in the water as well as the amount of use of the filter. Well water is more likely to contain contaminants not found in publicly treated water and may need even more frequent filter changes. As a rule of thumb, the filter should be changed every 6 to 12 months.
Failure to change these carbon-block filters allows contaminants to saturate the filter, forcing the filter to leak contaminants into the processed water. In a nutshell, after the life of the filter has expired, the water you are drinking may be even more contaminated by bacteria and impurities than what you were drinking without filtering your water in the first place!
Remember, your ice is also affected. It comes from the same source. So, if your ice becomes smelly, cloudy, or has little floaties, it is time to change that filter!