Like many hippie health trends that then go mainstream, a lot of it seems to filter in from Rastafarian traditions, where in the Ital diet they believe that alkaline water coming from the Blue Mountains in Jamaica (and other natural springs there which are naturally alkaline) help detoxify the acids in the body.
Not really. In the US at least, there’s the “Lead And Copper Rule”, which effectively requires utilities to adjust water composition to make the water minimally corrosive to copper and to lead. This often involves delivering water at a pH higher than 7. (San Francisco, for example, has water pH near 9, although it seems to be on the high end compared to other systems.)