water Article Modelling Domestic Water Use in Metropolitan Areas Using Socio-Cognitive Agents Antoni Perello-Moragues 1,2 , Manel Poch 1 , David Sauri 3 , Lucia Alexandra Popartan 1, * and Pablo Noriega 2   Citation: Perello-Moragues, A.; Poch, M.; Sauri, D.; Popartan, L.A.; Noriega, P. Modelling Domestic Water Use in Metropolitan Areas Using Socio-Cognitive Agents. Water 2021, 13, 1024. https://doi.org/ 10.3390/w13081024 Academic Editor: Stefano Alvisi Received: 16 February 2021 Accepted: 26 March 2021 Published: 8 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 LEQUIA, Institute of the Environment, University of Girona, 17004 Girona, Catalonia, Spain; tperellom@gmail.com(A.P.-M.); manuel.poch@udg.edu (M.P.) 2 IIIA-CSIC Artificial Intelligence Institute of the Spanish National Research Council Campus UAB, 08193 Bellaterra, Catalonia, Spain; pablo@iiia.csic.es 3 Department of Geography, Autonomous University of Barcelona (UAB), 08193 Bellaterra, Catalonia, Spain; david.sauri@uab.cat * Correspondence: luciaalexandra.popartan@udg.edu Abstract: In this paper, we present an agent-based model for exploring the interplay of basic struc- tural and socio-cognitive factors and conventional water saving measures in the evolution of domestic water use in metropolitan areas. Using data of Barcelona, we discuss three scenarios that involve plausible demographic and cultural trends. Results show that, in the three scenarios, aggregate out- comes are consistent with available conventional modelling (while total water use grows, per capita water use declines); however, the agent-based simulation also reveals, for each scenario, the different dynamics of simple policy measures with population growth, cultural trends and social influence; thus providing unexpected insights for policy design. Keywords: agent-based modelling; policy-design tools; scenario simulation; water use modelling; socio-hydrology 1. Introduction Climate change is posing severe threats to socio-ecological systems [1,2], in particular the water domain, especially in terms of water security and hence social welfare [3–5]. Addi- tional pressures are of various kinds (e.g., population growth, cultural changes, and ageing infrastructure) and thus the challenge on water governance and management becomes all the more essential. Besides the direct impact of these foreseen changes, water management will have to face the increased complexity which arises from the dynamic interdependency of these factors [6]. Consequently, anticipating these future trends and designing policies to cope with them becomes a key management requirement for both companies and public regulators. This paper is concerned with the task of sifting through the interconnections of the socio-cognitive, demographic, and technological factors that are involved in domestic water use in order to design adequate policy interventions. For instance, reducing water use may be necessary to increase the socio-economic system’s resilience and sustainability, but driving the system towards this end would need concomitant investments and social practices that may entail new regulations, incentives and cultural change as well; this puzzle should then be translated into policy instruments and tested. In this context, exploring the water use trends that urban areas will exhibit in the near future is fundamental. Increasing evidence indicates that domestic water use in many cities of the developed world has declined during the last decades [6]. Water pricing and taxation, technology-based efficiencies, and rising environmental awareness by citizens may be cited as the most significant reasons behind this decline. However, population concentration in urban areas is expected to increase from 55% up to 68% by 2050, which will entail a higher water demand [7]. In particular, demographic trends point towards smaller families and single households [8], which leads to smaller housing units and, as a consequence, to a Water 2021, 13, 1024. https://doi.org/10.3390/w13081024 https://www.mdpi.com/journal/water