Just a little anecdote about water storage. We had occasion to stash a gallon of water (unanticipated surplus) in a very isolated, hot, arid, inaccessible location (archeological site) that we knew we would return to. The water was simply tap water, untreated in any way.

Indeed, a year later we returned to the location. Apprehensive about our stashed water, we cautiously tried it. It was fine. It had been exposed to temps ranging from 0F to 100F, but had been shielded from direct sunlight. The container was a reused Clorox bottle,so it probably did get a bit of clorination. I still change my water at regular intervals, but if I miss a change, I don't sweat it. You can always filter and treat.