Hmm, I see that the same CDC website also says “observe the expiration date for store-bought water” and so does the Red Cross. Argh. well, it sounds like the FDA has been studying the issue pretty thoroughly and they are the ones who are charged with regulating bottled water.
Note though that if you take your own water from the tap or another source and store it in your own bottle, all bets are off. There’s no guarantee that you will have safe water to drink after 6 months; it depends on the condition of the water and the composition of the container or liner that you use. Also, everything I’ve said is based on US standards and I can’t vouch for its accuracy if applied to other countries. Nonetheless, if you are buying bottled water in the US or of comparable quality standards, hopefully this information has quenched your thirst for knowledge.
3/10/14 update: The San Francisco Chronicle ran a story today about a study in which some BPA-free plastic products were still observed to contain chemicals with similar potential
effects as BPA. The study hasn't undergone peer reviewed publication (it is based on toxicology reports from a commercial lab and a lab at UC Davis), and the products tested are gimicky sippy cups that change color, so it's difficult to infer whether this is relevant to those BPA-free clear plastic water jugs. Moreover, your emergency water will be used for just a few days rather than drinking questionable water daily for years. However, given the relevance of the recent report to the findings presented in this blog article, I wanted to mention it for the sake of providing a balanced picture.
10/16/14 update: It's advisable to not store your emergency water bottles in hot areas; a shed in the middle of the back yard in the sun is probably not a great idea. This may increase the chances of the plastic breaking down in as yet unknown ways.
You may be interested in reading the subsequent article that I posted on 10/16/14 about whether or not portable water filters can substitute for stored emergency water (they can't).