Well, how much are you planning on drinking on a daily basis? If you're planning on storing water long term, a canteen isn't the way to go, IMO.
For long term storage, you're better off with water barrels. Factory water bottles will store for awhile as long as they are kept out of light and heat. They never were meant for long term storage. Water stored in barrels will last awhile, but may start to taste funny as it becomes deoxygenated. Stir it with something clean to help with the taste and avoid purchasing an aerator, unless you just have the money. With power loss, your back to running a pump by hand, if you've bought one, or stirring by hand. Take a look at Aqua Paks.
Reliance Aqua-Pak 2.5 & 5 gallon Water Container
or
Reliance Aqua Tainer Water Jug
Drums
Water Storage and Water Filtration
Gravity filter
Monolithic Marketplace - Just Water, Ceramic Drip-Filter
Here is a link to some info by Dr. David Manz on sand filtration of water in developing countries
Manz Water Info | David Manz
The bottom of that link has manuals and guides on how to build one.
I have also seen rain barrels for sale at Ace Hardware stores.
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