filtered
Any water filter that takes out both minerals in particular "cacium" as well as chemical/biological impurities will do, when you are shopping around, take note as to what the filter does, and doesn't do. The mineral end is just to help eliminate deposits which can not only cause your equipment to break down, you lose overall volume and of course, have a residue that will create a bad taste. The rest is for taste, as a rule, if the water is bad, no matter how good your equipment you'll never get a superior cup of joe.