The solution diffusion model was fitted to the experimental data to obtain values for 𝐴, 𝐵 and 𝑘 "# , however, a satisfactory fit could not be yielded (see SI Section S7). The obtained best fit of the solution diffusion model yielded model parameters that significantly overestimated 𝑅 for large 𝐽 ! , indicating that, in addition to transmembrane diffusion, solute is being dragged across the membrane by the solvent, and suggesting the need to include a convection term in the transport model. Accordingly, a more suitable fit was obtained when fitting the Spiegler-Kedem model (Eq. 10 and 11) to the experimental data. The obtained best fit was found by arranging the model equations as Π = 𝑓(𝐽 ! ) and 𝑅 = 𝑓(𝐽 ! ), and finding the parameter values that minimize the RMSE sum between data and predicted 𝑅 and ΔΠ for all measured 𝐽 ! via the minimize functionality from the python scipy.optimize package. The resulting values for 𝐴, 𝐵, 𝜎 and 𝑘 "# yield an acceptable description of the investigated RO system (Figure ).