I'm sure your brother is indeed a very smart man.
I might point out that tap water is provided by local municipalities. So, the quality can vary greatly from town to town.
I lived for several years in one town where they performed lots of tests to verify that the water was as pure as they could make it, short of distilling it. Every year we got a print-out of all the things that they had tested the water for. It tasted great.
My mother lives in a community where for many years they didn't bother to tell anyone how pure the water was. It tasted like sulphur. It was ghastly. And brown. Yuccch. (They've since improved the water!)
Bottled water often is simply local water from the tap. Really. It often isn't anything special.
My suggestion is to see if you can find out how clean your local water is, and, if it seems to be reasonably pure, then continue to enjoy it.
As for purified water, I use a Brita filter for making my tea, as the minerals in the tap water make the tea taste less than pleasant. Otherwise I drink my local water straight from the tap.