Maybe this is a bit of an unusual spot, but it is very local. We are incredibly proud of our fresh tap water, me of course included.
The tap water in Ljubljana is not only good but also refreshingly cold. And the best part is that it is easily accessible, at least in the centre. There were public drinking fountains already in the past, but since Ljubljana was titled European Green Capital in 2016 there were many more installed.
Keep in mind that there is a smart phone app, TapApp or Tap Water Ljubljana and a web page that have all public drinking fountains marked on the map.
The new ones are more or less the same, but I have two favorite ones among the older ones. One is at the Congress Square, representing an old well which was at the same location but between monastery walls at that time, and the other, the one on the picture, is by the cathedral.