Proton exchange membrane fuel cells (PEMFC) represent one of the most interesting technologies for powering automobiles or small portable electronics. The repartition of water inside the fuel cell, as well as its microscopic organization inside the membrane are critical issues that impact fuel cell performance and durability. These properties change depending on the amount of current that is drained from the cell, but also of the history of the membrane. SANS is one of the best suited tools to study these issues as it informs on both water microstructure and organization, but also because measurements can be performed while the fuel cell is functioning in a non-intrusive fashion. Here, we propose to study the water distribution inside a functioning fuel cell in order to understand how local current density and membrane ageing affect the distribution of water in the PEMFC. This study could allow us to understand why PEMFC with aged membranes see a drop in performance, but also why some parts of the cell perform better than others. This information could help us adapt operating conditions so that we can have fuel cells with better performance and durability.