Data on the tritium abundance in precipitation, the Sava, the Danube and water bearing layers at the Sava alluvium in Belgrade region during 1976–88 are presented. Tritium content in precipitation mostly fluctuates from 1.1 to 18.3 Bq/l. Similar values between 0.4 and 16.8 Bq/l were obtained in the Sava and in the lower layer (17–30m), while in the upper layer they were different depending on the location and hydrogeological characteristics of the aquifer on the right and left bank of the Sava, ranging between 0.0 and 12.9 Bq/l. In the Danube, the content was about 20% greater than in the Sava with occasionally extraordinary high amounts up to 63 Bq/l. In the Danube, the content was about 20% greater than in the Sava with occasionally extraordinary high amounts up to 63 Bq/l. Measuring tritium, temperature and level of ruer and grounduaters (Ranney-wells, shallow and deep piezometers from 8 to 30 m) a hydrological relation river aquifer of different intensity was found; very strong between the Sava and Ranney-well and weaker with the upper layer. Variations in temperature, levels and tritium concentrations in the piezometers and especially in the Ranney-wells follow those in the Sava with a time lag of a few or about ten days.