The water supply I am on has deep wells for the source, so it has minerals from all of the ground up rocks left by the glaciers. The municiple supply takes out the iron, but that is it. Carbonate is really high, about 290 ppm. That is why I use RO.
If you are in another part of the country, you might be blessed with soft water. I will attach a map of water hardness. Be aware that the Great Lakes are really pretty soft, and many cities such Chicago, Detroit, Cleveland as use those as a source.
I am in the really dark green area in southern MI.