Water activity measures the quantity of water in a product to make sure bacterial, yeast, and mold growth is not supported. By measuring the water activity in a cannabis product, it provides an excellent way to analyze how susceptible the product is to microbial contamination. The higher the water activity value is in a cannabis product, the more freely water can be used by microbes as a food source or to support chemical and enzymatic reactions which lead to spoilage.
This unfortunately affects the longevity and safety of the plant material. In an effort to control spoilage due to microbial contamination, water activity levels for usable cannabis must be less than or equal to Aw 0.65.