Not necessarily true. It is down to water hardness, which tends to be an east/west thing. East tends to be harder, and hence crap for hot drinks. So down here Cornwall and Devon have soft water, so presumably good for making drinks. Dorset, where I live, is sadly a bit harder, although the tap water is drinkable, unlike London water. There are water hardness maps online (I tried posting a link but my phone said "no").