The water distribution of a Nafion-based membrane in a direct methanol fuel cell was analyzed in-operando using high resolved synchrotron X-ray radiography. A specially developed fuel cell design that meets the requirements for radiography as well as for stable cell operation was used. Different electric loads were applied during cell operation. A correlation between the electric load of the cell and the thickness of the membrane was found: the membrane thickness increased with increasing current density. The impact of local water drop dynamics on the water distribution in the membrane and the electrodes have been analyzed. We found a strong influence of water drops in the cathode channel on the water distribution in the adjacent area of the Nafion membrane. (C) 2015 Elsevier B.V. All rights reserved.