Question:
Replacement is a matter of policy, it is insurance just like the stored water itselfThat is utter nonsense for any reasonable definition of "long durations". Have you ever canned peaches or pears?

Answer: Water can also be canned and then it is preserved for a very long time. And that is if you want certainty. Want to play the odds a bit? Unlike Vegas, most will win...

I pump water out of a hole in the ground that has supposedly been there for many years, then I drink it with no treatment whatsoever. My folks live in a small town that pumps water said to be several thousand years old, aka "fossil water," and distributes it thru the town without treatment. I'd consider that "long durations." Consider that water was on the ground since it was last distilled yet is totally potable today.

I also have two 55 gallon drums downstairs that I filled from my well in 2001. I was going to refill them last year, but the water was still perfectly fine so I left it as it was. I did put a few CCs of clorox in each barrel for insurance as I was filling it. But mostly the cool and the dark do the job. If I fill a clear soda bottle with water and leave it on the kitchen counter (think light) for a couple of months, it fills with something organic...