Unless a bottle of water claims to be from a spring, or a particular source, then its just a bottle of water, which can be from anywhere, probably the mains supply.
Of course, there is nothing wrong with drinking tap water, so there is nothing wrong with drinking tap water from a bottle, if you want to pay for it.
Personally, I dont buy water unless I am desperate and somewhere where I cant get tap water, but if you do want to buy water, why does it matter where the water is from ?