Abstract: Water supply in aircraft for on-board use in conjunction with water outlets in lavatories and a galley, includes a waste water tank connected to at least some of the waste discharge outlets on board of the aircraft; a water purifying plant connected to and receiving water from the waste water tank; and a fresh water tank having outlet means, connected at least to some of the water outlets, and having an inlet connected to said water purification plant, for receiving therefrom purified waste water; an additional tank for drinking water may be provided as well as a separate supply line therefrom leading to drinking water outlets on board of the aircraft.