Tea is mostly water and so it makes sense that the water used to steep a cup of tea must be healthy and free of chemicals. Another important fact is it must have oxygen, because oxygen helps release the flavor of the tea leaf.
In this modern day you can purchase all types of water, spring, purified, distilled, de-ionized, mineral, public (filled with chemicals), and well (which may have sulphur and chemicals). Distilled water is so oxygen lacking that it will corrode a pipe and many people will describe its’ flavor as dead and flat. Not a good choice.
Keep in mind, if you like the flavor of the water by itself, that does not mean it will make a good tasting tea. There is much more involved than the flavor of the water that creates a delicious tea. Try making two cups of your favorite tea using two different types of water, for example, using tap water and purified water. The taste difference can be dramatic.
I have had guests at my tearoom, fall in love with a particular tea I have served them. They will purchase some for home and the next day come back to say there must be something wrong with it because it doesn’t taste anything like what they had in my store. My first questions is always, “do you have city water”. To date, every person has answered “yes”. I explain that the chemicals in public water will change the flavor and if they use a water filter or purchase purified water, they will enjoy their tea.
At my tea room, The Confection Cottage, we filter all of the water coming into our building, which contributes to the great flavor of our foods, teas and coffees.