Zero times in ‘how to build a municipal water system’ class in engineering school were any comments made about hard water being healthier, so I too would like to know.  I guess maybe you could argue that soap works better?  Guess that means mineral springs are bad for you?

Plenty on chlorination, ozonation, sand filters, RO systems, max contaminant levels,  denitrifying dirty water out the back end of the system, and how to actually soften the water, but never a comment on the health implications of softening it.