Cogeneration applied to very high efficiency thermal seawater desalination plants should reduce the cost of desalinated water to a level more than competitive compared to the reverse osmosis technique for potable water. This is even more the case for process distillate water. In this article we present an original concept of cogeneration relating a gas turbine to a multi effect desalination unit + a lithium bromide absorption heat pump. We take as example a 9 MW gas turbine related to a 9600 m(3)/d (2.54 mgpd) desalination unit. The specific heat consumption of the desalination unit is 35 kWh/m(3) and the estimated cost of distilled water at outlet of the plant is, under reasonable economical conditions, less than US $0.5/m(3).