I buy 5 liter bottles of mineral water.
I have about 12 such bottles in my cellar.
When I have drunk 2 ou 3 bottles, I replace them.
I recently (last month) started to stock bleached tap water, using the 5 liter empties, to have an extra stock on hand, if need arises. Clutter considerations will limit this stock to another 12 bottles.
I intend to rotate this bleached water every 6 months/1 year (not sure which, yet).I won't drink it except to test if it's still OK, but will use it to flush the toilet (I don't want to waste water)