Wetlands located in cities are among the most diverse and productive natural based systems which provide important benefits such as water quality improvement, flood control, soil erosion protection, recreation opportunities, support for wildlife and natural products. This paper presents the water budget in Văcărești wetland in order to provide an overview of the hydrological processes that make wetlands unique. Văcărești wetland is located in south part of Bucharest city and represents the single urban Natural Park in Romania. The existing wetland has been formed on an area conceived initially as the bottom of an artificial lake where the nature and the wildlife developed on their own. Using historical data and several algorithms, this paper presents the analysis of the water budget on the considered area which would lead to a better assessment of the hydrological processes. The goal of the study was to gain knowledge on how the wetland is sustained and, as a result, to develop solutions to prevent the ecosystem deterioration conducted by external pressures like climate change with extended periods of droughts or anthropic influences.