Neat Scottish whiskies and the local source water used for and during whisky production have been analysed for their H-2 and O-18 isotopic composition by High Temperature Conversion-Isotope Ratio Mass Spectrometry (TC/EA-IRMS). With coefficients of determination R-2 for delta H-2 and delta O-18 of 0.71 and 0.88, respectively, measured delta H-2 and delta O-18 values for water used in the production of Scottish whisky were found to be well correlated with the delta H-2 and delta O-18 values observed for the corresponding whiskies. By plotting bulk H-2 against bulk O-18 isotope abundance data of authentic whisky and counterfeit whisky samples it was possible to discriminate between samples of authentic whisky and samples of counterfeit whisky. (C) 2012 Elsevier Ltd. All rights reserved.