The predominant source of all dissolved oxygen contamination of the condensate and feedwater is air and due to the high solubility of carbon dioxide, it undergoes equilibrium reactions with water resulting in substantial amounts being absorbed in water. To combat this, steam from the turbine is condensed and leaves as condensate, creating a vacuum which draws air into the condenser. This article explores the principles of condensate control and Metrology and Analytical Technology and testing air inleakage.