The benefits of bioretention systems are very important to the environment. Because of low knowledge in the field at a national level (in Romania), they are not promoted or implemented. The aim of this research was to develop and promote bioretention systems in Romania, with particular reference to one of the biggest urban developments: Cluj-Napoca. We used the RECARGA to determine effective models of bioretention cell for environmental conditions provided by 4 types of urban sites: commercial, industrial, high-density residential, and low-density residential areas. The bioretention modelling was made for a single event, with and without underdrain. The variables considered in the simulations were: native soil texture, hydrological conductivity, CN, and percentage of impermeable surface. Soil texture was one of the main variables that influenced the model, and is the most important element of control in the design and performance of the bioretention cell. The results also show that hydraulic conductivity has a large effect on the duration of flooding in the bioretention cell. All the details related to a bioretention cell must be carefully studied, and included in the numerical modelling in order to obtain viable bioretention systems.