Groundwater plays an important but often overlooked role in the hydrological functioning of large metropolitan areas. In the Greater Montreal region (population 4.1 million), dense urbanization, extensive underground infrastructure, and a long history of groundwater abstraction have profoundly altered natural flow systems, complicating groundwater characterization. The current project was designed primarily as a knowledge acquisition initiative, aiming to improve scientific understanding of groundwater systems rather than to deliver operational management tools. The objective of this presentation is to examine the challenges underlying urban groundwater studies and to explore the integration of diverse data sources. We describe the logistical and methodological challenges of collecting primary data in a dense urban environment, including the scarcity of suitable existing wells and constraints associated with installing new monitoring infrastructure. Considerable efforts were required to reconcile fragmented historical datasets from multiple governmental agencies and consulting reports into a coherent, standardized database. Urban infrastructure exerts strong anthropogenic control on groundwater dynamics. Subsurface networks , underground transportation systems, tunnels, and deep foundations act as hydraulic barriers or unintended drains, modifying flow patterns, temperatures, and contaminant transport pathways. To address these complexities, conventional regional-scale characterization methods need to be adapted, for example with enhanced spatial sampling targeting infrastructure-influenced zones, refined geochemical tracer selection to distinguish urban signatures, and modified numerical modeling incorporating subsurface infrastructure as boundary conditions. We conclude by discussing how methodological adaptations and carefully structured datasets support informed decision-making across the urban community and provide a reproducible framework for groundwater studies in other dense metropolitan areas