An analytical solution of water mass balance equation was obtained considering diffusion and electroosmotic drag fluxes under non steady state regimes. The theoretical predicted profiles in a membrane electrode assembly were compared experimentally in a single polymer electrolyte hydrogen/oxygen fuel cell changing operating conditions such as, flow velocity, current density and temperature. The specific anodic and cathodic areas were calculated using the carbon monoxide anodic stripping method (ca. 17000 cm2). The electroosmotic drag coefficient was determined with electrochemical isopiestic methods showing temperature invariance, i.e. 2.3 between 313 and 353 K for water contents less than 5, but when reaching 20 it increased to 3.2. Polarization curves were attained galvano dynamically in a single fuel cell showing a strong dependence on water residence (performing with distinct water amounts and conditions). Internal resistance (0.59 to 0.24  cm-2) and open circuit potentials (0.90 to 0.38 V) were affected by water reduction (from 0.8 to 0.4 units). Continuous water recycling of the fuel cell was adopted to preserve the shape and characteristic parameters of the fuel cell under full operation with excellent results.