The present invention discloses a metal hydride compressor for reducing energy wasted in the reversible heat pumping system and the method of controlling the water flow in the reversible heat pumping system for operating the metal hydride compressor. The metal hydride compressor comprising of two or more compression modules, each of which comprising a gas tank; a plurality of gas tank; a first and a second water tank of a reversible heat pumping system to act as the cooling water tank or the heating water tank; a cold water reservoir tank and a hot water reservoir tank of the reversible heat pumping system to supply cold/hot water to the water tanks through a first three-way valve and receive cold/hot water from the water tanks through a second three-way valve ; and two or more inlet ports and outlet ports , each having a ball valve connected to the compression modules. The gas tanks are submersed in a cooling water tank or a heating water tank of a reversible heat pumping system, so that at least one module, when being cooled, is absorbing hydrogen at low pressure while at least another module, when being heated, is desorbing hydrogen at a higher pressure. The water is directed to flow from water reservoir tanks to water tanks and then is directed to flow back to the origin water reservoir tanks using three ways to conserve energy needed for heating and cooling the water in the reversible heat pumping system.