I agree with some of the other FTers that putting the divide on national level makes little sense.

I can safely say that Slovakia is on 5 on the scale, except for some of the small villages without municipal water, where the situation varies between 3 and 5 based on house-by-house well quality, mostly hovering around 4. Same goes for Hungary etc.

Romania I would definitely bump up to 4, probably 5, for those places with municipal water. Many of the systems are new, and water sources are generally high quality in the Carpathians.