AbstractTo further the understanding of the relationships between past climatic conditions and the hydrogen and oxygen isotope composition of old groundwaters, a study of the relationship between the composition of daily rainfall and meteorological parameters at a single site was made. The composition of daily rainfall was found to be extremely variable, with little seasonal dependence, and with no clear relationship to daily mean air temperature. This is typical of a maritime climate, although the site studied is located on the east coast of England. The most important control on composition is the origin of the precipitating air mass, whether Atlantic or Continental. The possibility of investigating past climates is discussed.