I seem to recall from the 50’s that adding bleach to stored water kept it indefinitely. I suppose you could not store it in plastic...need a tank of some kind. Has this been debunked?
I take just-emptied 2 quart juice bottles, wash them out, fill 7/8s up, and then freeze them in our deep freeze. I figure as long as the power holds up they should be good forever.
I store my water in bulk using tap water which is cheaper than bottle water and surprising often cleaner and/or the same water used in main bottle waters, in 5-15-55 gallon containers and simple switch it out by using older containers to water my plants and garden then refill them adding a few drops of bleach and then placing a last fill date with a dry erase marker. Water is arguably the most important prep you need to store and is also the bulkiest, but without adequate clean water no amount of food will keep you alive long.