Filter water from RO system into a Zero Water pitcher...
Pros: Cleanest tasting water
Cons: Have to buy filters/ and change them every couple of months. (I buy the 4-packs, lasts me a year)
https://www.amazon.com/ZeroWater-ZD-018-Filter-Pitcher-Quality/dp/B003QXM3U8
I use a counter top 2-cartridge water filter that is connected to the faucet spout.
https://smile.amazon.com/dp/B07GBNB7VG/
I tend to fill 64oz Ball mason jars with this to keep in the fridge.
The Zero Water branded filters also perform very well, I have an older smaller size version of this that uses the same filter:
https://smile.amazon.com/ZeroWater-ZD-018-Filter-Pitcher-Quality/dp/B003QXM3U8/
I will admit this is an obscure option, but how about never descaling the machine? You may have to if you have been running tap water through it for a while. I have been running nothing but purified water since I first turned mine on. I plan on never descaling my machine. I use this ZeroWater pitcher to clean my tap water. I swear by it. It beat Brita and others hands-down. I recommend one if it is available in Germany.
https://www.amazon.com/dp/B003QXM3U8?ref_=cm_sw_r_cp_ud_dp_E04KF2X74EC0RB7PTWKT&th=1
Edit: shorten URL