This paper aims to provide a historical reading of the urbanization of the water cycle in Madrid and Barcelona. Starting from an urban political ecology view, the urbanization of the water cycle is understood as the mobilization of water resources to keep pace with and sustain urban growth. This process could not be understood without inquiring into the evolution of the urban fabric in both cities. At the same time an understanding of the power choreographies over the water cycle needs to be brought to the fore. In Barcelona, disputes between the municipality and private capital over the water monopoly deeply shaped the trajectory of the urban supply from the mid-19th century until the early 20th century. Later on, under private monopoly, the search for water resources beyond the urban limits required the development of infrastructures such as dams and channels to keep pace with the intense urbanization of the postwar period. On the other hand, the fully public nature of the supplier in Madrid may help to explain the impressive magnitude of the waterworks, which belittle the urbanization of water of the Catalan city, while showing that ‘modernity’ in the form of ample supplies of good-quality water arrived in Madrid almost 100 years before Barcelona. Recent environmental and economic crises bring to light the hidden, complex and fragile entanglements that permit the flowing of water into the urban and suburban fabrics.