Water transport properties in polymer electrolyte membranes are a subject of interest in studying low temperature fuel cells. This is because these membranes require the presence of water to be conductive for ion transport. One important water transport mechanism is water diffusion. This mechanism is characterized by the water diffusion coefficient which is strongly dependent on local water content. There have been many approaches proposed to measure or calculate the water diffusion coefficient for different membranes. Some of the more established techniques include sorption, permeation, and nuclear magnetic resonance (NMR). Unfortunately, disagreement between reported values exists. The technique used in this work involves the use of a permeation experiment where the diffusion coefficient is determined through coupling a numerical model with the data from the experimental rig. The process was first applied to Nafion, a well-known and widely used proton exchange membrane (PEM), for validation purposes. The calculated diffusion coefficient as a function of water content agreed well with NMR data from the literature with such agreement being rare, especially across different techniques. Once the process was validated it was then extended to SnowPure Excellion, an anion exchange membrane (AEM). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3585834] All rights reserved.