Updated: Jul 28, 2020
We recommend reading the owners manual of your make of coffee maker and following the manufacturer's recommendations. In addition, here are a few general tips which apply to all charcoal filters in coffee makers:
Charcoal filters (or activated carbon filters) are used in coffee machines mainly to target chlorine in brew water. SCA (Speciality Coffee Association) recommends that there be 0mg/L of chlorine in water as it negatively impacts taste of brewed coffee.
The life of filter will depend on quality of supply water (from a chlorine content perspective) and volume of water which passed through it.
There is no easy way for a user to tell when the carbon filter’s life is over other than by taste or smell of the filtered water.
The presence of chlorine in water can be detected with more certainty, compared to just taste and smell, by using a chlorine water test kit for aquariums or drinking water. They are super cheap (~50cents) and very commonly available. A handy kit to have in the house.