So does this mean that Water bottles that you buy in the store are good for longer than it syas on the box? If so, is the "expiration" only for taste purposes?

Not necessarily, all bottled water may not be filtered and/or treated and therefore an expiration date may be just that an expiration date. Water, for long-term storage should be purified/treated/filtered, not only to remove organisms, but various chemicals. Bottled water quality can and will often vary considerable from bottler to bottler and even lot to lot. The source of the water will have a lot to do with what chemical and organic materials may be dissolved in the water. Mineral or spring water will by their very nature may have substantial minerals (chemicals) and organics dissolved in the water. These minerals can interfere with the chemical disinfection process of the water, if that is the method the bottler uses for disinfection.

Water, one might purchase from a supermarket where they have a self-serve bottle filler, is likely nothing more then water from the city/town’s municipal water source that travels though a pre-filter, charcoal bed filter and may finally pass through a UV treatment device (for bacterial/viral/fungal). In fact a lot of bottled water is nothing more then municipal water that is passed through a device described above, but on a commercial grade level.

With that all said it is still probably okay to drink water from a sealed water bottle well beyond said expiration date. It is still likely equal to or better then water from a questionable water source. One could always boil or treat/filter the bottled water if in any doubt.

Pete

Unlike tap water, bottled water is relatively lightly regulated. I'm not sure if there is even a uniform definition of "expiration date" when it comes to bottled water.

I think it's safe to drink bottled water well beyond the expiration date. And, if in doubt, just purify it when you use it.

One point that others have raised in the past based on their experience is the durability of the containers long-term. The soft, HDPE jugs don't seem to hold up well over long periods of time, developing pinhole leaks. PET bottles will probably do better than HDPE, but for long-term durability and avoiding surprise leaks, a more heavy-duty water containter may be preferable.

There is a purpose for the expiration date, but they won't tell you this. They want the politically correct people to believe that they have to discard the water after the expiration date so that they will buy more, increasing the company's profits. If the water is clean potable water to begin with, there should be no dangerous organisms in it. If it is kept closed, any microbes there will not have any source of fuel, thus no multiplying. Storage in a opaque container will stop the source of energy that is used by algae type life (light). Water can't decompose like organic chemicals such as drugs can, so it doesn't have an expiration date. I filled my water storage in January, when our tap water is odorless. In the summer, our tap water sometimes smells faintly of swamp or chlorine.
The only thing that may happen to water is plasticizers leaching from the plastic container that it is in. I have water that I stored in a 30gal. opaque food grade drum 3 years ago. I checked it recently & it tastes & looks fine. Don't check it too frequently. Each time that you open it is a chance of possibly contaminating it. There are no chemicals in it other than the chlorine used by the municipal water people, so I will have to use clean food safe containers (not the bucket from the garage).