Tap water with carbonic acid - but right!
Who, like me, has an excellent tap water without aftertaste, is well served with carbonated machines. But it has to be done right. Above all, you should, especially in the summer, in the refrigerator pre-cooled water use (bottle immediately refill, then you have it always ready). Cold water can absorb more carbon dioxide and last longer.
The prejudices against tap water have all been dispelled, so they do not need to be reheated. Of course, mineral water companies say something else, but they have to. In any case, I do not carry boxes anymore (live on the 2nd floor).
