I live in San Francisco where our water is mostly snowmelt from the Sierras (Hetch Hetchy) or pretty neutral water from a few city wells.
SF PUC does often add a pretty heavy dose of Chloramine, so the water does need to be filtered, (and there is sometimes a bit of off flavor,) but mostly a quick trip through a britta or maytag filter is all that you need to get it ready for tea.
After a bit of filtration, the water here is very neutral and ready to let almost any tea shine without much effort.
Other areas of the world, it can be a bit more challenging. For example, I grew up in the Midwest in an area where all the water came from wells tapping into limestone aquifers. The water there was horrible for tea. I spent much of my young life trying and trying to make a good cup of tea and failing over and over.
I recently visited an area of California where the tap water comes almost exclusively from volcanic mineral hot springs. The water there is so mineral laden that the it nearly tastes like tea just coming straight out of the tap.
The hotel where we stayed even filtered it heavily through the device pictured above. I spent several days futilely trying to get a good cup of tea out of it, even with teas that I was familiar with from home.
I suppose it is interesting, as in China mountain spring water is most often highly thought of for tea brewing, the most famous, of course, being that from the “Dragon Well” in Long jing, which is said to be very heavy in texture.
But, I don’t really remember the tea there tasting like anything but tea leaves in water.
In any case, it’s always good to remember that tea is 99.99% water. If the water doesn’t taste good, the tea you make from it won’t taste good either.