Fick's law of diffusion is widely used for analyzing water migration behavior in food bodies. However, the occurrence of irregular water content profiles in starchy food when analyzed by Fick's law has been reported. In order to describe these instances of seemingly irregular water migration behavior, the Water Demand Model was proposed. In this paper, the thermodynamic basis of Water Demand Model is examined using a polymer solution theory and a mechanism by which a resistive pressure is formed to stop water ingress in a food body. It was found that Water Demand Model needs a minor modification. The modified Water Demand Model, i.e. Relative Water Demand Model, is found to work well when it is applied to simulate the change of water content profile in a wheat flour dough slab in which water migrated against the gradient of water content. (C) 2007 Elsevier Ltd. All rights reserved.