We compare differential, integrated and stopping electronic cross sections for (non-relativistic) proton impact in liquid water calculated by two different optical-data models using reflectance and Compton scattering data. The complex dielectric response function over the energy–momentum plane is obtained by a sum-rule constrained extended-Drude scheme, which fits the optical data and preserves the Bethe ridge. Higher order Z-corrections were implemented for extending the stopping calculations down to the Bragg peak. The construction of molecular cross sections allows the contribution of each electronic channel to the stopping process to be calculated and the need to separately evaluate the shell corrections is overcome. The present study complements our previous work on the influence of dispersion to proton inelastic characteristics and provides further insight on the application of the dielectric methodology to proton electronic losses in condensed biological materials.