Moisture is a parameter closely related to microorganisms, because, like all living beings, they use water to transport nutrients and energy elements through the cell membrane. The ideal moisture of the compost is around 55%, although it varies depending on physical condition, size of the particles and the composting system. If moisture drops below 45%, microbial activity decreases, the degradation phases cannot be completed and hence, the resulting product is biologically unstable. If the moisture is too high (> 60%), water will saturate the pores and interfere oxygenation through the material. In processes in which the main components are substrates such as sawdust, wood chips, straw and dry leaves, the need for irrigation during composting is greater than in wetter materials such as kitchen waste, vegetable, fruit and grass clippings. The optimal moisture content for composting is 45% to 60% water by weight of the base material.