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• Water consumption of felt-based living walls and involved variables were assessed. • 16 living walls located in different Spanish cities monitored during 1–4 years. • Annual average water consumptions between 2.5 and 9 L m-2 d-1 were recorded. • Values in line with the quantity of water required for other green infrastructures. • The orientation and exposure to incident radiation identified as the key factors. Living walls are vertical building integrated systems that allow increasing vegetation in cities, providing many benefits. However, some concerns are raised involving their environmental sustainability given that they need to be irrigated, especially in warm climates. Little information is available regarding the quantity of water required for the adequate maintenance of the vegetation in these vertical greening systems. This study aims to quantify the water consumption of felt-based living walls and assess the influencing variables. To do so, 16 living walls located in different Spanish cities were monitored during 1–4 years. Annual water consumptions between 2.5 and 9 L m-2 d-1 were observed, which are in line with the quantity of water required to irrigate other green infrastructures. Though obviously the climatic conditions and species selected had an influence on the water consumption, the orientation and exposure to incident radiation and plant density were identified as the key factors. When possible, recirculating systems are advisable to reuse the excess of drainage water recovered from the bottom of the living wall. [ABSTRACT FROM AUTHOR]