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The influence of water shortage on the water extraction pattern has been quantified for periods of water stress. A macroscopic water extraction model combined with the Richards' equation was inserted in the numerical simulation model HYSWASOR, to test four different water stress functions. Input parameters were obtained from the literature and derived from extensive measurements of alfalfa, under well-controlled conditions in a greenhouse. Results indicated that a linear reduction function could not fit the experimental data range satisfactorily. Most of the existing nonlinear reduction functions could only fit a part of the data range, while best agreement was obtained with a nonlinear two-threshold reduction function. Parameter values obtained by calibration differed only slightly from those of the experiments. The heterogeneity of matric potential over the root zone did not play a significant role in water uptake. Roots appeared to take up water from relatively wetter parts of the root zone to compensate for water deficit in drier parts. The main reason for small discrepancies between measured and simulated water contents appeared to be water uptake during darkness over the stress period.