At the present time the available models of water uptake by roots of crops do not take into account the root growth. These models solve the set of equations that govern the system on fixed domains (Molz, 1981). A Recent model that takes into account the simultaneous connection between nutrients uptake and root growth (Reginato et al., 2000) by means of the formulation of a moving boundary problem that solves the system of equations for a moving domain (the growing root system). In similar form, for the process of water uptake taking into account the plant as an organism in constant growth a moving boundary model for water uptake is formulated. In this communication we will report some theoretical results with respect to the water uptake model for plants growing mainly in clay soils. The plants grows in fixed volume of soil (as in flowerpots). The model is solved by means of the application of the method of dominion immobilization and later application of finite elements method. Under these conditions diagrams of sensitivity for soil and plant parameters are obtained.