Pure water is best water
When brewing a nice cuppa it is always better to use water from a good source. Ideally spring or filtered. Water from the tap can be highly chlorinated and laden with impurities like chalk and limestone. To know tea has been brewed with good water you need only look at the colour.
A good brew will always create tea with an orangey-reddish hue, while tea brewed with less desirable water will turn an unpleasant shade of brown.