One-third of the samples exceeded the California standard or the industry's own purity guidelines, or both, for a chemical or bacterial contaminant. There are no federal mandatory standards. About one in five samples contained industrial chemicals, and some samples contained arsenic, nitrates or other inorganic contaminants. In both cases the levels generally were below state or federal standards. Though bottled water is generally considered to be good quality, the industry is controlled by self monitoring.
Bottled water does have an expiration date.
Make sure you check for this when purchasing. When you think about it, it's comparable to taking a bath with 75 - 100 of your closest friends. Wherever they've been and whatever they've been exposed to gets dragged into the pool with them. Usually chlorination takes care of most of this problem. For the most part, outbreaks are caused when children have bowel movements in the water.