A simple solar water heating system comprising an unglazed textile-plastic absorber and an uninsulated plastic accumulator tank with thermosiphon flow of heat transporting fluid has been tested under outdoor conditions. The unglazed textile-plastic absorber is very sensitive to changes in climatic conditions. The overall efficiency and the response time to changes in irradiation depend also from ambient air temperature, absorber temperature and intensity of solar radiation. Under good conditions its efficiency is comparable with that of sophisticated metallic collectors (e.g. with selective absorbing layers), but on cold days when the intensity of solar radiation is low it is considerably lower. For some applications, where only a small rise in water temperature is needed, such as swimming pool water heating or water preheating for irrigation in greenhouses, they may be more cost effective than metallic solar collectors, when their low price is taken into account.