A steady-state, two-dimensional model is presented and discussed that describes the water transport in a proton exchange membrane fuel cell. Concentrated solution theory is used to describe the transport of water in the membrane, and of water vapor and liquid water in the electrodes. The inclusion of the liquid water transport into the model turned out to be essential for explaining recent experimental results on the effective drag coefficient and its dependence on operating conditions as well as on variations of the components that constitute the membrane electrode assembly.