All good information, I store my water in food grade 55 gal drums. People seriously underestimate the amount of water they need or plan for long term water shortages. You need water for hygiene as well, poor hygiene and improper waste disposal will lead to a lot of other problems that can kill you.
If you store large amounts of water and fail to maintain it's purity even after many years it will most likely still be less contaminated than what you are going to find after a natural or man made disaster and will be easy to re-purify. You can also just change the water when you change your smoke detector batteries if it gives you peace of mind.
I had a thought have a 55 gallon water heater tank that your water line goes in and out of. It would seem that the water would stay fresh. Some folks throw electric ones out if the elements go bad, if it is glass lined it should last a while I'd think.