I buy 5 gallon "boxes" of water at Sam's Club. These have 2 2.5 gallon dispensers in them. The best before date is roughly 2 years after the time of purchase. right now, my water says "best before 7/7/2011" and I bought them about 9 months ago.

And as a perk, the boxes can be stored 4 or 5 cubes high. The "spout" style bottle is not overly durable, but the master cartons are double corrugated. One reason I chose the "spout" style is that it easy to operate without wasting water. With children in the house this is desirable.

For people who have the ability to purchase water in this way, its hardly worth doing any testing, research, or paying "extra" for water containers at the prices you can water that will last for 2 years "off the shelf" for pennies a gallon.

Granted, if you are in the country this is not a viable choice for you.

As another irritating thing to think about:
I was reading in a consumer reports magazine that the shelf life is actually much longer than this. If I remember the article correctly, the state of new jersey put a maximum on the "best before" date, to ensure product freshness/safety for its consumers. The major manufacturers, apparently eager to have a reason to cycle water faster, adjusted their production process to "comply". Later, the state of new jersey repealed the requirement, but bottled water companies still put a conservative 2 year expiration because 'their machines were set up this way'.

To verify this I did a quick search on CR (of which i subscribe online and on paper) but many of the printed articles do not appear online.

However, a googling of new jersey bottled water law turned up instant verification of some of what I have said, as seen here, for example.