The evaporation process in a four-effect still for the desalination of sea and brackish water was experimentally investigated for typical operation conditions in ZSW's thermal process laboratory. Different operation modes and configurations of the test facility were examined: heat recovery, natural and forced convection in the distillation chambers (effects). The results show that heat recovery from the outlet mass flows of concentrate and distillate has only a little effect on distillate output but the gained output ratio (GOR) increases considerably. With blowers and intermediate screens, installed inside the distillation effects the distillate yield can be increased by more than 50% and the GOR by 60% related to results of a configuration without heat recovery and blowers. This reduces the specific thermal power requirement and thus the required solar collector area and boiler capacity.