The objective of this work is to study the impact of the air supply of a fuel cell system on the humidification and water management issues. The first study consists in defining an indicator of the humidification state, which represents the output air moisture content and quantifies the quality of the water management. This indicator is evaluated both in simulation and experimentally. It is shown that it can be used in real time to improve the energy management and control of the fuel cell. Specifically, taking into account the air moisture in the air supply energy management is a mean to avoid major defects like fuel cell flooding or electrolyte membrane drying.