Preservatives are used in consumer cosmetic products in order to stop microbial growth and to provide product stability, thereby helping to ensure safe products for the consumer. The water activity of a system can be useful for determining microbial contamination risk and preservation factors. For example, decreasing water activities by adding water-binding agents tends to reduce microbial growth in a product. The water activity of several commonly-used industry preservatives was measured at supplier-recommended levels of preservatives using a commercially available water activity meter (Decagon Aqua Lab Series 3TE). Previously created products were also tested for water activity, and the results were compared with their USP micro-challenge test results. It was determined that most commonly-used industry preservative systems did not affect the water activity of the products they were in. Also, known water-binding agents, e.g. glycerin, affected water activity more than the preservative, itself.