Insanely Long Water FAQ. The short of it is that some water hardness improves espresso flavor, and there is an optimal range balancing between taste and regularity of machine maintenance (descaling). This range depends upon how many drinks you make.

Charcoal filters, like Brita, don't reduce water hardness. You will have to get some sort of true softener - I'll leave it to others to advise you. I don't soften my water.

This might sound silly but every setup needs a mascot sitting on top. Keep those evil espressos away.