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Things You Drink Can Be Used To Track You
sciencehabit writes with an intriguing story about the potential of figuring out where people have been by examining their hair: "That's because water molecules differ slightly in their isotope ratios depending on the minerals at their source. Researchers found that water samples from 33 cities across the United State could be reliably traced back to their origin based on their isotope ratios. And because the human body breaks down water's constituent atoms of hydrogen and oxygen to construct the proteins that make hair cells, those cells can preserve the record of a person's travels. Such information could help prosecutors place a suspect at the scene of a crime, or prove the innocence of the accused." Or frame someone by slipping them water from every country on the terrorist watchlist.
http://news.bbc.co.uk/2/hi/england/bristol/10332975.stm
Basically some bones from a German cathedral could be places as having lived in England due to isotopes in the teeth.
This helped confirm the bones were of a 10th century English princess.
This may be forensically useful, but don't think of it like a fingerprint or a DNA match. There's only one degree of freedom here -- whether the water is isotopically "heavy" or "light". All of a person's water co9nsumption history is mixed up into one number.
So you won't be able to tell the difference between, say, a person who lived all year in Illinois (with a moderate isotope ratio) and a person who flies back and forth between Montana and Florida (who'd have a mix of "heavy" and "light" water in their system.)
"Is there a timestamp attached to those water molecules?"
Well, there sort of is. Hair grows at the root only, so if I watch how the patterns change moving from the root of a hair to the tip, I can get a fuzzy sort of timeline of your waters' origin. Circumstances where that's precise enough to be useful, though, seem narrow.
1) Water at spring A has more calcium (a mineral) than water at spring B
2) Because of this, and some chemical processes, the water at spring A has a higher percentage of heavy water (deuterium oxide) than the water at spring B (this has a 50%+ chance of being incorrect, but let's stick with it for the example's sake)
3) Person X consumes water from spring A and person Y consumes water from spring B.
4) The metabolisms of the two persons break down the water and put it into the proteins in their respective cells.
5) Person X has more deuterium in his cells than person Y.
Hope that helps clear things up.
Another fun but pointless fact: tin foil isn't made of aluminum.