In this study it is shown that there is a relatively low optimum feed water temperature to a SWRO plant to maximise the lifetime production of a typical B10 permeator. This is based on the calculation methods outlined in the Dupont Permasep Manuals The results tend to indicate that in the case of these particular membranes and in typical Middle East conditions, there is little advantage to be gained from preheating the feed water to a SWRO plant such as might be attempted in a distillation/reverse osmosis hybrid seawater desalination plant.