How long can you keep water in tank?

For those using bottled water instead of using public water hook-up for drinking, cooking, etc. I checked on the label of some of the water sold in the stores and it was from a city water source. No difference.

A few years back there was a report on TV by a investigating source that stated that out of six most popular brands of bottle water only three were equal to public tap water and the other three were not as pure as tap water.