This study aims to propose a holistic, life cycle assessment (LCA) of urban wastewater systems (UWS) based on a comprehensive inventory including detailed construction and operation of sewer systems and wastewater treatment plants (WWTPs). For the first time, the inventory of sewers infrastructure construction includes piping materials and aggregates, manholes, connections, civil works and road rehabilitation. The operation stage comprises energy consumption in pumping stations together with air emissions of methane and hydrogen sulphide, and water emissions from sewer leaks. Using a real case study, this LCA aims to quantify the contributions of sewer systems to the total environmental impacts of the UWS. The results show that the construction of sewer infrastructures has an environmental impact (on half of the 18 studied impact categories) larger than both the construction and operation of the WWTP. This study highlights the importance of including the construction and operation of sewer systems in the environmental assessment of centralised versus decentralised options for UWS

ICRA authors also acknowledge the Marie Curie EU Reintegration grants 2010-RG-277050 and PCIG9-GA-2011-293535, the EU-ITN SANITAS (ITN – 289193), the Spanish government (CTM 2011-27163; RYC-2013-14595) and the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group (2014 SGR 291)