[Groxx]

The article mentions using only hydrogen and oxygen isotopes (I'd assume due to the distortion caused by filtering if you did it by any other elements), and looking at hair samples to detect the isotopes in the proteins / molecules which make it up. Even being carnivorous is going to distort things if you get your meat from multiple locations (say, fish. That comes from everywhere, at least for me), as you'll incorporate the amino acids (which have plenty of H and O) into your own proteins.

After looking closer, it appears that the study makes only the (obvious) claim that bottled water purchased near location A has similar isotopes to water in location A, due to bottling habits. Though I haven't read the study itself. The article may be entirely vague speculation, to drum it up into something more exciting / inflammatory.