That's not exactly news. Unfortunately. Its common knowledge that (in the western world) tap water is generally purer than bottled water.

I seem to remember at least one report, on this forum, of so called bottled water being refilled and resealed by the locals. You cannot exactly blame them. By their standards its good money for relatively little effort.

One good thing about is that you are most likely to be dealing with bacteria and viruses rather than protozoa. Which can be dealt with by chlorination.