•First fully automated on-line SPE–LC–MS/MS determination of UV filters.•Method suitable to determine UV F of a wide range of physicochemical properties.•Sensitivity achieved allowing trace UV F determination in several water matrices.•First determination of UV filters residues in groundwater. This paper describes the development and validation of the first fully automated method, based on on-line solid phase extraction–liquid chromatography–tandem mass spectrometry (on line-SPE–LC–MS/MS), for the determination of UV filters (UV F) and transformation products, with a wide range of physicochemical properties. The developed method was validated and applied to the analysis of the selected compounds in river water (RW), groundwater (GW), influent and effluent wastewater (IWW and EWW). Comparing with the off-line methodologies published so far the presented method provides several advantages including a shorter extraction time, lower sample volume and minimum manipulation. Low limits of detection were achieved for all the studied matrices, <3ng/L (GW), <3.5ng/L (RW), <4ng/L (EWW) and <10ng/L (IWW), allowing a reliable and accurate quantification of the analytes at trace level. SPE optimization and critical aspects associated with the trace level determination of the target compounds (e.g. matrix effects) have been also considered and discussed. The method was successfully applied to the analysis of the UV F in five real water samples of each considered matrix, being the first time that these compounds were determined in GW.