One of the most commonly used proxies in the interpretation of paleoclimatic records is the isotopic composition of oxygen. Its variability in these records depends on the isotopic composition of precipitation in an area. The isotopic composition of oxygen in precipitation is influenced by altitude, latitude, continentality, temperature, amount of precipitation, but also by the moisture sources of precipitation. The aim of this paper was to determine the moisture sources of precipitation over Zagreb city based on meteorological data. Also, the share of recycled moisture in the total amount of precipitation (resulting from evaporation above the continent) was determined. Five-day back trajectories of air masses for days with precipitation> 0.5 mm at the Zagreb location was determined using the HYSPLIT model of NOAA (National Oceanic and Atmospheric Administration) based on data generated by GDAS (Global Dana Assimilation System). The analysis of the obtained data calculated the locations where the air masses absorbed moisture, and the spatial analysis of the obtained data will calculate the share of recycled precipitation in the total amount of precipitation.