Water permeabilities, driven by concentration or pressure gradients, through NRE211 and catalyst-coated membranes are reported, and the effect of the catalyst layer (similar to 18 mu m thick, 30 wt % Nafion ionomer, carbon-supported Pt, 0.4 mg Pt cm(-2)) on membrane water permeation is deconvoluted. For the system studied, water permeation is limited by the bulk membrane; the effect of the catalyst layer was insignificant and, despite catalyst layers being deposited on the membrane's surface, it does not influence the rates of sorption or desorption at membrane interfaces. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3357339] All rights reserved.