The flux of liquid water through Nafion membranes of different thickness and equivalent weight was measured as a function of hydrostatic pressure and temperature. Hydraulic water transport across Nafion membranes increases with temperature and equivalent weight of the Nafion. Hydraulic permeability increases with temperature due to both decreased water viscosity and increased hydrophilic volume fraction. Convective flow from the applied hydrostatic water pressure is an order of magnitude greater than the estimated diffusive water flux associated with the water activity gradient. Water sorption and hydraulic permeability data predict a hydrophilic pore network with hydrophilic domains 2.5 nm in diameter spaced 5.5 nm apart. The pore network structure from water sorption and hydraulic permeability are consistent with the spacing between hydrophilic domains observed with small angle X-ray scattering experiments. (C) 2011 Elsevier B. V. All rights reserved.