Unlike “wet” anaerobic digestion systems, the dry one has been poorly investigated. The objective of this work was to investigate the influence of the water content on the anaerobic reactor performances and on the microbial populations. Different concentrations of total solid (TS) were tested in batch conditions: 10, 15, 20, 25, 30, 35%. Four replicates were performed for each . The biogas production and composition were monitored. A relatively fast kinetics of anaerobic digestion was observed at 10, 15, and 20% TS with a minimum production of 149 ml of CH4/ volatile solid VS (g). Reactors operated at 25% TS and two replicates of 30% TS showed an intermediate biogas production rate with minimum production of 101 ml of CH4/VS (g).Very low rates were observed for two replicates at 30% and at 35% TS with a maximum output of 35 ml of CH4/VS (g). Two behaviours at 30% TS, suggesting that this value could represent critical moisture content. Microbial investigations showed a specific pattern of the microbial community structure in the reactors having the lowest performances.