A mobile reserve of firefighting water comprising: - a shipping container having a front wall, rear wall, top wall, bottom wall and side walls, the outer surface of the bottom wall being intended to rest upon the ground; - an endoskeleton arranged inside the shipping container and designed to reinforce the inside of the shipping container; - a waterproof flexible membrane designed to be suspended inside the shipping container such that it can be changed from an initial position in which the membrane is substantially opened out flat, to a suspended position in which the flexible membrane is substantially folded to take on the shape of a suspended pocket and intended to form a reservoir to hold water, wherein - the endoskeleton comprises a main portion and a removable portion, the removable portion of the endoskeleton being secured to the main portion of the endoskeleton via removable securing means and, when the flexible membrane is in the suspended position, the removable portion of the endoskeleton is configured to absorb all or some of the forces applied by the pressure of water on the inner surfaces of the side walls, characterized in that the flexible membrane comprises a plurality of fastening holes configured to allow the passing of all or some of the removable securing means therethrough when the flexible membrane is in the suspended position, and characterized in that: - in the suspended position, the flexible membrane has an upper opening in the direction of the top wall of the shipping container, and - when the flexible membrane is in the suspended position, the removable portion of the endoskeleton is arranged inside the reservoir. - a shipping container having a front wall, rear wall, top wall, bottom wall and side walls, the outer surface of the bottom wall being intended to rest upon the ground; - an endoskeleton arranged inside the shipping container and designed to reinforce the inside of the shipping container; - a waterproof flexible membrane designed to be suspended inside the shipping container such that it can be changed from an initial position in which the membrane is substantially opened out flat, to a suspended position in which the flexible membrane is substantially folded to take on the shape of a suspended pocket and intended to form a reservoir to hold water, wherein - the endoskeleton comprises a main portion and a removable portion, the removable portion of the endoskeleton being secured to the main portion of the endoskeleton via removable securing means and, when the flexible membrane is in the suspended position, the removable portion of the endoskeleton is configured to absorb all or some of the forces applied by the pressure of water on the inner surfaces of the side walls, characterized in that the flexible membrane comprises a plurality of fastening holes configured to allow the passing of all or some of the removable securing means therethrough when the flexible membrane is in the suspended position, and characterized in that: - in the suspended position, the flexible membrane has an upper opening in the direction of the top wall of the shipping container, and - when the flexible membrane is in the suspended position, the removable portion of the endoskeleton is arranged inside the reservoir. characterized in that the flexible membrane comprises a plurality of fastening holes configured to allow the passing of all or some of the removable securing means therethrough when the flexible membrane is in the suspended position, and characterized in that: - in the suspended position, the flexible membrane has an upper opening in the direction of the top wall of the shipping container, and - when the flexible membrane is in the suspended position, the removable portion of the endoskeleton is arranged inside the reservoir. - in the suspended position, the flexible membrane has an upper opening in the direction of the top wall of the shipping container, and - when the flexible membrane is in the suspended position, the removable portion of the endoskeleton is arranged inside the reservoir.