The proponents of a change in water and wastewater infrastructures point to the advantages of decentralizing urban water at
neighborhood or building scale. This would include separation and resource recovery and reuse at point source, rainwater collection and
treatment, and implementation of green infrastructures and nature-based solutions with low energy requirement to manage rainwater and
combined sewer overflows. In this context, the so-called third route or extreme decentralization stands out as an appealing approach. The
concept foresees the integration of building-scale water recycling within cities that already have centralized water systems, which makes it
attractive given its compatibility with existing water governance. It enables water systems to adapt better to water stress without the need
to abandon current infrastructure or make substantial investments to move away from existing approaches. However, despite the
increasing evidence on the benefits of this paradigm shift urban water management, which would outweigh potential risks, the adoption of
decentralized water solutions in Europe has been slow. To address this, D-PATTERN is an ambitious project aiming at building an
integrated simulation and decision-support platform, merging experimental research with social science and modeling. It will draw on a
comparative analysis of two distinct urban case studies Girona and Santiago de Compostela to ensure a broad, applicable
understanding. It involves analyzing spatial and social variables of the case studies, implementing a pilot study for decentralized water
treatment to evaluate its feasibility, scalability and potential urban impact, and using advanced modeling tool, including Agent-based
Modelling, to simulate various decentralization scenarios. The research effort culminates in creating a Decision Support System that
extrapolates case study results into practical planning tools for widespread application of decentralization strategies. Through the synthesis
of quantitative and qualitative data, D-PATTERN aspires to advance knowledge into the societal factors shaping water management. This
comprehensive approach can influence policy and strategic planning, fostering the uptake of decentralized water solutions, attuned to
societal needs and contexts.