The water existence is essential to preserve membrane of PEMFC well-hydrated but accumulation of excessive water in channel leads to flooding and performance loss. In current research, the water management in cathode channel of a single-serpentine transparent PEMFC is studied for different stoichiometry, RH and temperature using direct visualization and image processing. An algorithm is introduced to quantify and classify the water and flow patterns in the cathode channel. The water coverage ratio is defined as measurement of liquid water accumulation in the total and local areas of channel. It is found that accumulation of water in the elbows is significant. Most of liquid water accumulates in latter channel rows near to gas outlet. The cathode stoichiometry has more effect on water management and cell performance than anode's. The effect of water coverage on cell performance is investigated. The time durations for first formation of important two-phase flow patterns in cell water management as fog/mist, slug and plug are calculated to obtain the time-scale of two-phase flow and water management. The superficial velocities of moving slugs and plugs are studied. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.