My stepdad used to work for a water company (I can't remember which one, but I'll ask him just so if I quote this in the future I can be accurate) and has a friend who handles water treatment for the county (dauphin, pa). The question he posed this treatment guy was "how long will tap water be storeable".

The response was basically several years. Now he said you'll get a thick sludge on the top or bottom of the water which you will want to separate away but the rest should be safe for drinking.

From what I've read on water purification this comes from fluc or coagulants.. these may be local to our area. From what I've also read it seems like you would want to go the extra mile and disinfect it upon taking it out of long term storage like this.

This is not an end all be all answer, though I thought some of you might find this information interesting.