It is my understanding that bottled water manufacturing standards include RO as part of their purification process, then essential minerals are added back to water in the latter stages.

So debating whether RO-ing already bottled water purified thru standard manufacturing process is senseless. On the other hand, planning to implement or install RO systems at home would be costly, since the level of water-hardness (due to inherent problems in operating distillation process in massive scale). RO-ing water running on the taps will be so great that you'd end up paying a premium (eg. replacing RO membranes every ±4,000 liters or so as is typical capacity for residential water purification systems) that any cost benefits will no longer be realized.