Water from the hot water tap on an espresso machine
The other day I decided to try filtered water versus non-filtered water for pour over coffee and the result was that the filtered water was better. This is not shocking since that was what I also concluded drinking the water straight, but since even our tap water is fairly soft and since coffee adds in a very strong flavor of its own it is not necessarily obvious that this would be the result. I could have just as easily believed that the subtle differences would be masked.
http://www.roaste.com/CoffeeBlogs/wakeknot/More-experiments-water
Source: http://www.roaste.com/CoffeeBlogs/wakeknot/Water-hot-water-tap-espresso-machine