How many days, or even weeks until a certain water inside the container (a tumbler, or maybe a 1 gallon water container) becomes undrinkable?  Does it vary on container? If so, I am using a plastic 1 gallon container usually found in water dispenser and my thermal tumbler.  Note that the water is in drinkable state before putting it in a clean container, I've asked this question because after a month of not using the water inside the dispenser I noticed that there are some tiny black particles at the bottom of the gallon container, I'm thinking that it might be contaminated.  *The dispenser is just a normal dispenser without any kind of filter  The water dispenser looks like this   
I am not aware of any official guideline on storing drinking water, probably because people just don't do it usually. But for other purposes of water storage (humidifiers etc.) the rule of thumb is that water which will sit around for more than a week has to be treated.   If anything, the rules for drinking water should be shorter (because you can have amoebas and other stuff, not just the legionellas risk from humidifiers) and not longer. So a week would be the upper limit, but shorter is better.  