<p>Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants widely detected in aquatic systems, yet their accurate quantification remains challenging due to strong temporal variability and ultra-trace concentration levels. Ceramic passive samplers (CPSs) represent a novel and promising alternative to conventional sampling techniques, offering time-integrated measurements while minimizing the influence of short-term concentration fluctuations. In this study, CPS devices were used in combination with liquid-chromatography/tandem mass spectrometry to determine PFAS in groundwater and river water within the Besòs River catchment area (Barcelona, Spain). First, CPS were calibrated for seven target PFAS under controlled laboratory conditions. All compounds exhibited linear uptake behavior throughout a 20-day calibration period, allowing the determination of compound-specific sampling rates. Laboratory blank experiments were also performed to evaluate background contamination and ensure reliable quantitative interpretation of field data. The calibrated CPSs were subsequently deployed in both groundwater and river water for 14&#xa0;days. Total PFAS concentrations ranged from 19.7 to 250&#xa0;ng L⁻¹, revealing widespread contamination across the study area. The concentrations obtained were consistent with those reported previously for the Besòs system and for other impacted European aquatic environments using conventional grab sampling methods. These results demonstrate the strong potential of CPS as an innovative and robust tool for quantitative PFAS monitoring in surface water and groundwater, providing reliable time-integrated concentration data and supporting their application in long-term environmental surveillance programs.</p> Graphical Abstract <p></p>