[hcarvalhoalves]

I don't know how it is in the US in particular, but in addition to Chlorine, tap water usually contains Al, Cu traces, lacks Ca and Mg and is low on bicarbonates.

So not only tap water already lacks compared to mineral, just letting it gas out, although can help with taste, is not enough to ensure quality, a filter is recommended. I don't know why you claim a filter is not necessary, I've never seen that.