Tracking Location Based on Water Isotope Ratios
…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.
Here’s the paper.