Water scarcity as a result of increasing population and limited fresh water sources, especially in certain part of the world, have developed an increasing demand for the seawater desalination. Among various desalination techniques, seawater reverse osmosis (SWRO) has become the most sought for technology due to its lower energy consumption over conventional distillation techniques, including multistage flash (MSF) and multieffect distillation (MED). However, SWRO desalination has still has high energy consumption and the brine (or concentrate) discharge from an SWRO plant is often problematic to the aquatic environment. Pressure retarded osmosis (PRO) is one of the most promising approaches that can simultaneously solve both problems, which utilizes the osmotic energy in SWRO brine. PRO can convert and/or produce energy from the salinity gradient resulting from the difference in the salt concentrations between two aqueous solutions. In this chapter we have investigated the feasibility of PRO, which utilizes several different water sources such as seawater, SWRO brine, and wastewater. In a practical application SWRO desalination plants, PRO can be retrofitted to SWRO plants as an energy recovery device and can utilize both the brine and impaired water from wastewater plants.