Cell humidification is an important factor affecting PEM fuel cell performance. A new cell was designed with slanted grooves on both cathode and anode sides to improve water management. Water transport measurements provided information on flooding, hydration, and back-diffusion. The results showed less water flowing out from the cathode side of an anode down-slanted channel than from that of a rectangular channel, because anode down-slanting induced a hydration gradient which caused water back-diffusion into the anode, leading to better performance due to improved membrane hydration and conductivity. At high humidification, performance decreased because of condensation and blocking of the gas diffusion layer, but replacing the rectangular channel with an anode down-slanted channel improved performance to match that of a rectangular cell at normal humidification. However, the cathode down-slanted channel showed membrane dehydration due to water draining away. Moreover, anode or cathode up-slanted channels. induced flooding, leading to poor performance. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.