"How can you tell where water really comes from?," Seed asks, provocatively. "It's always constituted of hydrogen and oxygen and is chemically identical throughout the universe," he explains. "Where things get interesting is when we start to consider the processes that water has gone through in different environments. We can measure the ratio of a heavy isotope to a light isotope e.g. δ18O:δ16O, which is the unique result of different biological, chemical or physical processes. For example, the ocean at the equator is warmer than at higher latitudes. This means you have higher energies at the equator so the heavier isotope is more likely to go through a process of evaporation. So, equatorial precipitation is isotopically heavier than polar precipitation because relatively more of the heavier isotope has evaporated into the atmosphere and turned into rain. As you move to higher latitude (towards the North or South Pole), the ratio of isotopically light to heavy water changes based on how the water evaporates and that can tell us whether it comes from polar areas, the equator or somewhere in between."
So, IRMS can tell us if water is really an ‘artisan’ product from a tropical source or whether it’s bottled and filtered water from a municipal tap in northern Europe, for example. It goes beyond just water, however. IRMS gives us a unique understanding of the biogeochemical processes that occurred during the formation of the component elements in the products we consume. This is valuable not just in a scientific sense, but also in telling us whether the food we eat and drinks we enjoy are actually what they say they are.