My two cents:
Bottled water essentially come in two varieties. The one with minerals added (like calcium/magnesium) and the one without (typically pure reverse osmosis water). For example the 25 cent per gallon machines you will find outside grocery stores are invariably just pure RO water and by far your best deal, but I guess you would need CalMag etc. The bottled water you buy inside the store will often (not always) contain minerals but it will say on the bottle (like "minerals added for flavor") but those are way too expensive and not worth it at several dollars per gallon usually.