Water and aqueous cations transport along multiple length scales in perfluorosulfonic-acid membranes. Molecular interactions in hydrophilic domains dictate nanoscale resistances while the connectivity of domains controls mesoscale transport. The developed multiscale models probes the synergy of these length scales. Concentrated solution theory and electrokinetics are used to predict transport in the aqueous domains as a function of hydration. A resistor network upscales the nanoscale properties to predict effective membrane ion and water transport and their coupling. The nature of macroscopic and nanoscale properties differs drastically because the mesoscale network mediates transport. Moreover, the effective tortuosity and connectivity is not the same for water and ion transport. The methodology and findings highlight improvement opportunities for membrane performance.