Abstract: A method for carbonating water and a carbonator which can be used on earth or in the microgravity conditions of outer space uses a tank having first and second chambers separated by a movable piston. Carbon dioxide inlets, water inlets and carbonated water outlets as well as agitators are provided for each chamber. The piston in the tank can be driven by introduction of either carbon dioxide or water into one chamber in order to reduce the volume of the other chamber and to cause carbonated water held therein to be discharged. Both chambers will be able to sequentially form carbonated water when both carbon dioxide and water is contained in one of the chambers.