This study concerns the hydrodynamic modelling of percolation and drainage cycles in the context of solid-state anaerobic digestion and fermentation (VFA platform) of household wastes (HSW) in leach bed reactors. The focus was made on the characterization of the water distribution and hydrodynamic properties of the bed. A numerical model, set up with experimental data, highlighted that the simple dual-porosity model was not able to correctly reproduce all the hydrodynamic features and particularly the drainage dynamics. The model was improved by adding a reservoir (immobile) water fraction to macroporosity and allowed to correctly simulate dynamics. This model enabled to explain more precisely the water behaviour during percolation processes and these results should be useful for driving either solid-state anaerobic digestion or fermentation reactors.