I think that one important ...

I think that one important factor is increased awareness and sensitivity towards water quality. People are moe aware of the potantial health risk of untreated water so they will turn to bottled water. In addition I would imagine that water quality of wells and rivers could be highly affected by increased human (e.g. industrial) activity. I think other reasons might be related to increased availability of bottled water through marketing and expansion of activities. Increase in available income since the 50s could also play a role.