When planning on storing water for a long period of time, there's always an area of stress that needs to be considered: what's the best method that I can rely on? You can either use an expensive method that has a shelf life of a couple of decades or you could use a method that needs to be replaced every half a year but is much cheaper and equally reliable. Check out the latter below.
A prepared survivalist should have plenty of bleach on hand anyways, so this method should be fairly easy for most people and the best part is that you get relatively fresh water using this method, rather than spending a small fortune on hundreds of gallons of water that'll be unimaginably stale (yet drinkable) when you eventually need to open it, at which point you'll need to replace it for the next SHTF situation. Just a little something to consider for your disaster plans.