The performance and durability of proton exchange membrane fuel cells are closely linked to effective water management strategies. Inadequate water balance results in polymer electrolyte membrane (PEM) dehydration or water flooding, both leading to performance loss and possible cell failure. Exploiting the contrast from liquid water absorption and transparency of dielectric materials, such as polymers, at terahertz (THz) frequencies, we apply a simple, compact THz imaging system to image water build-up in the flow channels of a THz-transparent fuel cell supported by high resolution optical gauging.