For those whose water source is a private well, "we recommend having the water tested. If levels are above 50 parts per billion, you might consider using bottled water or changing the depth to be deeper or shallower." And though it will clear your water of many other contaminants, says Wilkins, "filtering will not remove arsenic."
In the second study, Valerie Garrett, MD, and colleagues with the CDC's Foodborne and Diarrheal Disease Branch were called in to track down the cause of a salmonella outbreak among infants in the southern Appalachian region, in the southeastern U.S.
The team eventually tracked the problem to a batch of bottled water processed at a large plant in North Georgia and marketed specifically for infant use. While the source of the contamination has not been proved beyond a doubt, Garrett says that local cave-dwelling salamanders are the likely culprits. These animals shed bacteria into local springs, and the plant in question had stored the processed water for bottling in the same tanks that had held spring water.
Most people who drink bottled water do so precisely because they think it's cleaner than tap water. But according to Garrett, "just because it comes in a bottle doesn't mean it's safe."
So how likely are you to be sickened by your next swig? Fortunately, not very.
"For your typical consumer, bottled water is probably quite safe," says Garrett. But those who can't fight off infection -- people undergoing chemotherapy or with advanced AIDs, the very old, and the very young -- "have to understand that bottled water is not sterile. They are at particular risk [of serious illness] from contamination of any water product, bottled or not," she tells WebMD.
Given that, says Garrett, those at high risk "might want to consider drinking chlorinated water or a water product that has a biologically active disinfectant in it."
If you're wondering where you might find such an exotic product -- consider your kitchen sink.
"Tap water [from a U.S. municipal source] has biologically active chlorine in it at the time of consumption. There is something actively killing bacteria as you put it in your mouth," Says Garrett.