Water activity is a fundamental property of aqueous solutions, and by definition is the ratio of the vapor pressure of the water in the substrate to that of pure water at the same temperature. The concept of aw has been very useful in food preservation and on that basis many processes could be successfully adapted and new products designed. Water has been called the universal solvent as it is a requirement for growth, metabolism, and support of many chemical reactions occurring in food products. Awhas its most useful application in predicting the growth of bacteria, yeasts and moulds. The purpose of the research is to study the water activity in various culinary preparations, and to determine the influence of the thermal treatment used (frying, baking, boiling), the concentration of sugar and salt on the aw and the shelf life of the products. The research methods used were the following: the experimental method that was carried out with the LabSwift-aw device, manufactured in Switzerland, which has a precision of 0.01 and the bibliographic research of scientific sources and the comparison of the results obtained.