Gas-water separation is a fundamental requirement during long term operation of manned and man-tended space systems. Two areas of specific concern are in cabin humidity and temperature control and in gas removal from cooling water loops.This paper addresses design and testing of breadboard models for a condensate separator and a gas trap. Both models are based on semi-permeable membranes as main functional elements. The breadboard designs are driven by the requirements of the COLUMBUS space station.The condensate separator shall remove heat as well as water vapour from a humid air flow. Water shall permeate through the membranes, that are separating the air from the cooling water.The gas trap shall filter gas bubbles in a water loop and release the gas from the loop. In addition it shall maintain dissolved gas levels well below saturation.Starting with a short outline of requirements and rationales for concept selection, the paper gives a description of the breadboard model designs. Test results of the ongoing study are presented.The development work is being performed in the frame of ESA's general support technology program (GSTP).