The analysis of the reconstruction of the drainage system was carried out for the existing drainage system of the city of Labin due to the deficiencies and damage of the mixed drainage system. Two variants were analyzed in the simulation program SWMM, variant A as a separate system with an underground tank and variant B through the implementation of green infrastructure measures. Bases and data from the Feasibility Study for the Labin-Raša agglomeration area were used, and based on them, a model was created for a particular variant. The results are presented in graphic and tabular form, by means of which economic, technical-technological, social and ecological items are valorized in addition to the solution selection criteria, and a more favourable variant for the area in question is selected. The objective of the analysis of the benefits of the reconstruction is to provide adequate defence and disposal of relevant rainfall, protection of underground aquifers and provision of an adequate quality of life for the population while revitalizing the ecosystem and hydrological conditions to the state before urbanization. For the mentioned area analyzed by the SWMM model, it was determined that option B with green infrastructure implementation measures is a more favourable option in the long term, providing adequate disposal of precipitation inflows by relieving the system of green infrastructure facilities while revitalizing the ecosystem.