Salinity gradient processes have a great potential to reduce the energy consumption in water treatment, especially when high salinity waters are in question. Even though the theoretical approaches for the salinity gradient processes are quite strong, there are still several issues before these processes can be applied in full scale. One of the most important challenges between theoretical and full scale applications is the development of commercial size membrane modules. In this chapter, we have summarised the previous approaches and attempts to develop economically feasible and thermodynamically efficient membrane modules. We have focused on the flat sheet and hollow fiber membranes, and their large scale applications. Flat sheet membranes have distinct advantages when it comes to engineering and optimising the support layer thicknesses and structures, however the spiral wound module design has a serious drawback based on the loss of active surface area. On the other hand, hollow fiber membrane applications, which have superior active surface area utilisation, are limited by the pressure drop within the fibers.