River runoff and the resulting water resources which provide the needs of mankind for fresh water are subject to variations in space and time mainly depending on the space and time variability of climate characteristics. Thus there are close interrelations between the problems of the provision of fresh water and the problems of both natural and anthropogenic changes in climate. Moreover, these interrelations are characterized by specific features both under natural conditions and during a period of man's intensive impact on water resources. The problem of these interrelations has acquired a particular scientific and practical importance during recent years in which climatologists have attempted to predict global anthropogenic changes in climate for the near future, changes unknown on our plant for millennia. The present paper has been prepared mainly on the basis of research results obtained at the State Hydrological Institute in Leningrad. It describes the global interrelations between climatic characteristics and water resources under natural conditions and in the case of intensive water resources development; up-to-date ideas on the anthropogenic changes of the global climate are given; the possible consequent effects on future water resources are analysed.