In a world with an increasing urban population, analysing the construction impacts of sanitation infrastructures through Life Cycle Assessment (LCA) is necessary for defining the best environmental management strategies. In this study, the environmental impacts of one linear meter of sewer constructive solution were analysed for different pipe materials and diameters used in Southern Europe; a unit of different sewer appurtenances (pump, manhole and inspection chamber) was also considered. The impacts of the pipe materials were compared considering different lifespan periods and high-density polyethylene (HDPE) turned out to be the worst option, being polyvinyl chloride (PVC) and concrete the most favourable ones. Few data are available on the material and energy flows in the installation stage; therefore, a comparative analysis of trenches with sand and concrete bedding was conducted. The results show that the installation stage represents up to 80% of the total life-cycle impact of the constructive solutions. Concrete pipes with half-concrete/half-sand bedding are the best option and produce 20-30% of the impact of HDPE pipes with concrete bedding. Hence, designers should focus not only on the pipe but also on the trench model. A methodology was presented to enable the impact aggregation of the different sewer elements, and Betanzos (Spain) was selected to conduct a pilot study in small cities. In the future, studies will need to incorporate the use and maintenance stage, as it is not standard and varies according to the physical features of the cities. Finally, this study provides basic concepts for developing eco-efficiency indicators.