Due to the distribution of water within the cell, including in the membrane, GDE and channels, total water content is segmented based on the geometric structure of the cathode flow-field into channel regions and rib regions. The water distribution in the rib region for representative stages #1, #2, and #3 is shown in Fig. , while the water distribution in the corresponding channel regions is mapped in Fig. . Almost all water is observed in the channel region. Similar distributions are observed for other sample points (see Fig. ), with a high correlation coefficient of 0.992 between channel region and overall water content. This value for the rib region is 0.829 (rib region water content changes at least follow the overall water content). The significant presence of water in the channels is due to changes in internal water content primarily achieved by directly switching between dry and humidified gases; under 100% RH, a large amount of water accumulates at the edges of the channels (Fig. ).