Tritium is widely dispersed throughout the atmosphere as water vapour, arising from cosmic ray interactions and as a product of thermonuclear explosions. The tritium becomes part of the hydrological cycle and is present in rainfall and surface waters from whence a proportion may enter the ground-water system. This isotope, of 12.26 y half-life, thus forms a useful “natural” tracer in the study of ground-water resources.

A rapid and relatively simple method has been evolved for the accurate analysis of deuterium in water over the concentration range 0·090% to 0·24% w/w using a conventional infra-red spectrometer.