This work uses a combination of two magnetic resonance imaging techniques to produce quantitative 1-D water profiles showing the in situ drying of a single drop of an industrial surfactant based mixture, which is used during the manufacture of detergent powders by spray drying. The determination of the local water content during such drop drying is useful in terms of identifying drying behaviour and kinetics, and for the validation and improvement of drop drying models which ultimately could be incorporated into a full simulation of a spray dryer. To this end, a simple diffusion model incorporating an experimentally determined diffusion coefficient that varies as a function of local water content is presented and compared against the experimental data. Good agreement was observed between model and experiment. (C) 2008 Elsevier Ltd. All rights reserved.