I know Technivorm does not recommend using water from an RO system. So I found this out AFTER getting the unit. Though my observation of it being some truly fine coffee was while using that water. But, in my respect to the Moccamaster gods I installed an entire new filtration system using good old plain Cherry Valley water straight into a dual filtration system with activated carbon block filtration (not a cheap cartridge BTW) and installed it for drinking and coffee. Our water is so hard it does not come out as liquid but very fine gravel

But the machine was needing lots of TLC, white crust formed everywhere. Coffee grounds not fully wetted. Yesterday I pulled the lines for that system and went back to RO. Results? This morning's coffee. MUCH better. Machine made far less noise, coffee rounds fully wetted, actual coffee smoother and far less acidic.
Sorry Moccamaster. Some water is just plain beyond too hard for use in the machine. If the RO water ever does cause any harm to the heating element I will simply buy a new element. Cheap and easily available online.
I guess I could have fed the filter system water from the softener. But, there is always that ever so slight (if any) issue of salt remaining. So while it may be perfectly fine (no salt) I just have a "nagging" doubt. So RO it is! Luvin my coffee once again