Dear Members, Although I am working on heavy elements isotopes, recently, I have been reading a little about lighter elements, and I wonder if somebody out there can help with the following. I came across an article where water samples are analysed for (delta) 18O to shed shed light on the origins of the water?!! I don't know what is meant by the origins of the water, and how could that be done from the isotopic analysis. If you could help with some more information, I'll be grateful. Regards Ahmed Dr Ahmed Ayoub Analytical Group Macaulay Land Use Research Institute Craigiebuckler Aberdeen AB15 8QH U.K.