Romania, has declared, by the Governmental Decision nr.352/2005, all its territory as a sensitive area. This implies that, for all urban agglomerations larger than 10.000 population equivalent waste water treatment plants (WWTP) with nutrient removal must be built or upgraded. This paper presents the results regarding the possible environmental impacts expected from the project for construction of waste water treatment plant in the City of Vaslui, with main focus on surface water. This research study includes assessment methodology, project description regarding the rehabilitation and extension of the Vaslui waste water treatment plant, data related to water resources, impact assessment on water and appropriate mitigation measures. The assessment of the impacts has been performed for the construction and operational phase of the wastewater treatment plant. The construction phase was subdivided into several phases, while in the operational phase the impacts are analyzed following the line for treatment of the wastewater and effluent production, the line for sludge production and drying process, sludge disposal in safety conditions considering the provisions of 86/278/EEC Directive and the line for biogas utilization.