The water activity was evaluated in 39 mixtures of water with 1-propoxypropan-2-ol (1-pp-2-ol) at T = 298.15 K using an indirect method which measures the system capacitance. A careful calibration of the apparatus and the many measurements in the water very-rich region have enabled the determination of activity coefficients of 1-pp-2-ol using the Gibbs-Duhem equation, the system being modelled using a 6-suffix Margules equation. Infinite dilution activity coefficients for the two components are presented together with their associated uncertainties. Excessmolar Gibbs free energies were estimated and compared with literature values for the aqueous system of 2-butoxyethanol, which is a structural isomer of 1-pp-2-ol. (C) 2014 Elsevier Ltd. All rights reserved.