Copper will react with the chlorine in tapwater and make an insoluble green scum of copper chloride.
Electrolysis with stainless steel makes highly toxic hexavalent chromium.
Platinum is astoundingly expensive, even for plating.
How expensive a filter is needed to remove 99.999% of the chlorine?
The thing with electrodes is that a fiftieth of a millimeter of non-condutive crap on the surface hugely reduces the effectiveness. Around here the bottom third of my kettle has a tenth of a mil of limescale.