Los Angeles ? Scientists have devised a way to determine roughly where a person has lived using a strand of hair, a technique that could help track the movements of criminal suspects or unidentified murder victims.

The method relies on measuring how chemical variations in drinking water show up in the hair of people.

“You are what you eat and drink, and that is recorded in your hair,” said Thure Cerling, a geologist at the University of Utah and lead author of the study published this week in the Proceedings of the National Academy of Sciences.

While U.S. diet is relatively homogenous, water supplies vary.

By measuring the proportion of heavier hydrogen and oxygen isotopes along a strand of hair, scientists can construct a geographic timeline. Each inch of hair corresponds to about two months, Cerling said.

Cerling’s team collected tap water samples from 600 cities and constructed a map of the regional differences. The researchers checked the accuracy of their map by testing 200 hair samples collected from 65 small-town barber shops. They were able to accurately place the hair samples in broad regions.

“It’s not good for pinpointing,” Cerling said. “It’s good for eliminating a lot of possibilities.”