Calcium is a dissolved element which means it cannot be filtered (in the traditional sense) out of water.  To remove the calcium, some of the options we have perform an ion exchange where the calcium is replaced with magnesium.

Magnesium in the water going into your coffee machine enhances the extraction as well as the flavour of the coffee.  Added to that is that magnesium is a necessary mineral for repair of muscles and energy in your body.

Depending on what water filtration you currently have will influence which of the following options will be most appropriate for your circumstances.

Note: The BWT FIlter System User Guide Can be Found Here.