Several Keurig models have conveniently built-in water filters within the water reservoir. If you find that you have one of these, you will still need to change the filter cartridge after 60 tanks ...

Keurig 3-Month Brewer Maintenance Kit Includes Descaling Solution, Water Filter Cartridges & Rinse Pods, Compatible Classic/1.0 & 2.0 K-Cup Coffee Makers, 7 Count© Amazon ...