Abstract: In this paper, it was attempted to describe the effect of temperature of the Sava River and geothermal anomalies on the groundwater temperature of Zagreb and Samobor aquifer using the statistical analysis of time data series. The analysis features data for the daily temperatures of the Sava River and groundwaters measured by the Meteorological and Hydrological Services (MHS). Following statistical methods were used: correlation method, linear regression method and cross correlations method, as well as the analysis of the maximum, medium and minimum temperature of groundwater. Results of the above mentioned data processing are presented in the form of coefficients, diagrams and maps. This data processing showed that the daily measurements of groundwater temperature are not conducted regularly, as they are conducted in intervals of several months. Furthermore, due to the use of incomplete sets of data, reliability of the results of the data processing is questionable. By analyzing maximum, medium and minimum temperatures of groundwater it was found that maximum temperatures range between 11.5 ˚C and 26 ˚C, medium range from 10 ˚C to 18 ˚C and minimum vary between 4 ˚C and 16.6 ˚C From map of isotherms for maximum, medium and minimum temperatures can be noted that, with the existence of certain anomalies, temperatures generally increase moving downstream from Samobor aquifer area to Zagreb aquifer area.