A physically based model is presented that describes the storage of rainwater on plant canopies. Founded on a microscopic treatment of interception and drainage, it accounts for the vertical dependence of these processes and reproduces the fact that drainage starts before the canopy is saturated. On the basis of theoretical results, a new equation for canopy water storage is proposed for use within land surface schemes as an alternative to the single-store model, combining the advantage of a physically sounder description with a negligible additional numerical cost. A sensitivity study performed with a land surface scheme hosting the two different models shows that the difference in latent heat flux simulated with the new approach and the single-store model can amount to several tens of watts per square meter. Finally, it is shown that the theoretical model reproduces the exact functional form of the empirical canopy drainage formula proposed by Rutter et al. <1971>. Not only does this fact inspire confidence in our model, it also opens perspectives for the measurement of certain parameters used in the new interception model. ¿ 2001 American Geophysical Union