Urban water systems (UWS) comprise both the existing freshwater ecosystems and the water infrastructure that humans have built to (i) collect, store, treat, and supply water for potable and non-potable uses; (ii) collect, transport, and treat the generated wastewater; and (iii) discharge treated or untreated water to freshwater ecosystems. Analysing UWS emissions, resources, and energy consumption in an integrated manner using life cycle assessment (LCA) is of paramount importance to make wise decisions at the urban scale reaching optimal design, construction, and operation. In this chapter we provide an overview of LCA studies applied to UWS and describe challenges in this field first as a state of the art and second through 3 case studies which balance construction and operation inventories and include different elements of the UWS. The evaluation of water management scenarios in cities becomes more realistic as more UWS elements are included; making conclusions about scenarios of one particular element without considering the entire UWS might lead to misleading conclusions as the elements impact each other in a cascading effect. LCA is well established for wastewater treatment and guidance is now available for practitioners. Similar guidance is needed for other UWS elements (drinking water production, wastewater reuse, etc.) and for their integration. © 2022 Elsevier Inc. All rights reserved.