A thermal desalination system adapted to produce distilled water from feed water which may be sea water, based on a forward feed evaporator made up of a main water feed line, a vapor feed line, a distilled water main line and any number of effect groups. The effect groups include any number of effects which in turn include vapor inlets, water inflow lines, concentrate outflow lines that drain into a common concentrate drainage line, a vapor and water outlet in fluid communication with the distilled water main line, and heat transfer means that condense part of an inlet vapor to produce the distilled water.