Anaerobic dry digestion technology has been successfully implemented in the treatment of agricultural wastes, to produce renewable energy. The presence and mobility of water may affect biodegradation and gas production during this process. Thus, the quantification of the water and solute movement through preferential pathways of wastes may provide useful information in order to improve predictions of dry digestion performance. Laboratory tracer experiments were performed on different agricultural wastes before and after anaerobic digestion to investigate and quantify water and solute transport process under steady state flow conditions. A conservative solute was used as water tracer, and thus this work was restricted to the study of physical non-equilibrium mechanisms. Experimental results and numerical modelling indicated a modification of water flow during degradation, which can influence the biogas production.