Water management is a critical issue in polymer electrolyte membrane (PEM) fuel cells, and water transport through the membrane, catalyst layer and gas diffusion layer has significant impact on the cell performance and durability. In this study, the mechanism of water transport processes in PEM fuel cells has been analyzed through 3-D unsteady non-isothermal simulations, along with a comprehensive examination of various modeling approaches in literature. It is shown that the finite rates of sorption/desorption of water in membrane affect the cell current output and the cell response time. Water dissolved in the membrane should be taken as the proper mechanism of water formation in the cathode of practical PEM fuel cells. Capillary pressure and relative permeability have significant impact on the distribution of liquid water saturation and transport, implying a need for their determination under specific PEM fuel cell conditions. (C) 2009 Elsevier Ltd. All rights reserved.