If you are traveling from Indian Railways, you should know that many sellers of Bottled drinking water (mineral water) are not selling genuine water bottle.
Many local sellers collect the used bottle from station and train and if bottle quality is good, in local area, they fill tap water in bottle and insert the cap with seal by force in bottle easily. They also have cheap plastic sealing machine to make plastic seal on cap of bottle.
In most of the licensed shop inside railway station, you will get genuine bottled drinking water. Check the plastic seal and cap carefully for originality.
Try to buy that brand of drinking water of which availability is less in that station.The chances of originality will be high for that bottle.
Never purchase drinking bottle from unrecognized or unauthorized sellers, you may fall sick after drinking water.
After drinking water, always crush the bottle, so that no body can use it without recycling.
If the bottle is genuine, quality of water is almost safe.
Plastic used in Bottled drinking water is of very low quality, long use may cause several disease including cancers.