Is it necessary to boil bottled water before giving it to a 8 month old? Surely bottled water that has a shelf life of a year can't have any bacteria in it, else it would not last a year at room temperature. So, is there any reason why it would need to be boiled before giving it to a baby?
I don't imagine you need to boil any water before giving to a normal 8 month old; by six months the baby's immune system is functioning very well. I can't say I've ever boiled water before giving to a child, though we didn't ever give water under six months.
However, bottled water unless 'distilled' can and does contain some bacteria. For example, this study showed higher bacteria levels in two thirds of bottled water brands than tap water in Canada, and similar US studies show one third to one half do.
The bacteria in the water don't grow much due to the lack of nutrients and oxygen; but as most bottled water are just filtered like tap water is (not distilled or boiled), they can still contain bacteria. They are subjected to similar tests as tap water in the US, although some argue that they are not as well regulated in many countries, and even the best regulated water contains some bacteria.
This is primarily a concern with the inmunocompromised, such as very young infants (< 3 mo in particular), and people undergoing some treatments for cancer in particular as they can kill off the immune system (why I initially learned this caring for a sick relative).
First off, everything has bacteria. It's pretty impossible to remove all bacteria unless you work in a highly sterilized environment. In this case, however, bottled water is mass-filtered and mass-bottled in bottling plants that undoubtedly contain bacteria.
No, you don't need to boil bottled water. Boiling water is necessary when you don't know the source of the water, the amount of bacteria, or the types of impurities within the water, i.e. stream water, which nowadays, depending on the stream, I wouldn't recommend drinking from (nevertheless giving it to an 8-month-old). Bottled water manufacturers submit their water to be tested just like any other food, usually vetted through their country's equivalent of the FDA.
Sidenote about water and small children
Don't give your child distilled water, ever. Also, don't give your child too much water. While drinking water is relatively benign for older children all the way up to adults, we usually take in a lot more salts than infants and toddlers. Drinking too much water can cause infants and toddlers to rapidly lose electrolytes which ensure that are intra/extracellular fluids stay conductive. An electrolyte imbalance in the body can have serious side effects including death if not treated quickly.
If you are concerned about your child's level of hydration, give them something like Pedialyte or heavily water-dilated low-sugar sports drinks.