Bottles and bottleneck

In Pakistnan, literate community is becoming concious of water quality and its usage. There was a time when people used to drink tap water but now bottled water,being supplied by different companies has become a trend in fashion.
Some so called companies are extorting money out customer's pocket but supply ordinary water. How one one can distinguish between a pure and impure water?This remains the bottleneck of the day here in Pakistan.