does anyone have an to why there are experation dates on bottled water? this came up as a topic of discussion in a focus group and no one knows the/an answer. CAN YOU HELp

That's basically right. Most bottled water is manufactured in a near-vacuum in order to keep the impurities out. Due to the microscopic pores in the plastic bottle, particularly near the cap, over time air (with its associated impurities such as bacteria) will get into the inner bottle's environment. While the "freshness" / expiration date is a good judge of the quality of the water, an equally valid method is the same as one would use on a melon -- tap it and squeeze it. If the bottle is not firm, then it is overly "ripe" in both senses of the word.

This is a particular danger if the bottle spent much of its time in an environment that is foreign to you. For example, if you live in the US and are drinking French water that is, say, 3 years old, then if it spent that 3 years in your cupboard, then the foreign material and bacteria that is in the water are components that you have already developed a resistance to, and so, it doesn't pose much of a risk to you. However, if it spent those 3 years in, say, France or some other place that is generally out of your daily travels, then there will be bacteria and other material which you have not developed resistance to, and so you will surely get sick upon ingesting it. Note that I'm not saying anything derogatory about foreign places, it's just that an American probably doesn't have resistance to those strains of bacteria. The same would happen to a French person drinking American water.

So, just remember to tap and squeeze to test for freshness and you'll be fine.

Though many people instinctively feel glass is better than plastic, this is not founded in medical fact. (I suspect these feelings stem from the same kind of luddite reactionary impulses that lead to protests against nuclear power or human cloning)

A recent Harvard Medical School study conclusively demonstrated that glass bottles tend to leach heavy metals and rare earth oxides (YbO2, for example) over a period of time. Products stored in glass for less than about 60 days are generally considered safe, but I would definitely go with plastic for anything longer.

More importantly, it is becoming increasingly clear that water is "dipolar" -- and is just NOT a healthy beverage. Keep it at arms length if you value your longevity!

this "Bacteria trough plastic" sounds weird to me.I do not know about PTFE (the plastic most bottles are made of if I remember well) to be permeable to anything bigger than a molecule.

I would rather guess that the bacteria are in beforehand or more likely that the water could have its taste altered over time, what with light, temperature and all making the different minerals interact with each other chemically...

Of course, there is a difference between ingesting "pure" water-based beverages, and ingesting water buffered and mitigated by additional substances. Alcoholic beverages, gatorade, red meat, etc, all are relatively safe ways to ingest water.

I would have to suspect that water will 'leech' from plastic containers as quickly if not faster than from glass. Particularly water that has been through reverse-osmosis and ion exchange filtration. If water is low in soluble ions, it will pick up whatever is near it.