I wondered this for a long while, but I’ve realized that I’m in a pretty privileged position. Where I live (the Netherlands) the tap water is not only drinkable, it’s actually almost indistinguishable from mineral water. Certainly for me at least. I’m not much of a traveller, but when I was in Oostende in Belgium I remember the tap water was absolutely vile. It was (or at least tasted like) desalinated seawater. Instead of hydrating and refreshing it tasted stale and salty. If that was the only water I knew I probably would be drinking more refreshing stuff like ice tea or cola all day as well. When I got back to the Netherlands my first glass of tap water tasted like heaven.