Cannabis-based products for both medicinal and recreational use are gaining in popularity and acceptance. However, if not handled properly, these products can pose a safety issue for consumers. Dried buds, extracted oils, or processed edibles with microbial contamination can result in allergic reactions, respiratory complications, or foodborne illnesses. From a quality standpoint, changes in efficacy and potency due to chemical reactions or structural loss can also result in poor product and lost revenue. Water activity is utilized as an effective tool in the food and pharmaceutical industries to maximize microbial, chemical, and physical stability. It provides this same safety and control to the cannabis market and it is important that cultivators and processors understand water activity and how to maximize its usefulness. Safety regulations for the cultivation and processing of cannabis-based products is currently handled at the state level, resulting in inconsistent recommendations. As a result, not all states currently require water activity testing of cannabis. However, based on its established relationship with common safety and quality modes of failure, it should be one of the most important analytical test run by anyone in the cannabis market.