I've read (and I don't know where) that tap water from a public utility requires no additional treatment, as it is already treated with chlorine-dioxide by the utility. I've also read that unopened, commercially-bottled water should be capable of being stored at least two years.

I've stored my own water before from the utility for more than 6 months with no ill effects. But the containers are expensive, rotation is a chore that needs to be remembered, and I don't really like the chlorine taste of our tap water.

These days I just buy 2.5 gallon pre-filled containers of spring water. We use the stuff anyway, going through as much as 10 gallons a week, so its no problem rotating even a large supply every 12 months. I don't think you could buy twenty 5-gallon empty containers for the $100 I pay for them full. The size and weight is more convenient to carry and store than 5-gallon or larger containers.

I've also left some at a camping lodge for weeks in the winter so they experienced freeze-thaw cycles, and they held up without leaking.