This water tank, now no longer in use, is set atop a tower made from stone, brick and iron. Built between 1907 and 1911 by the engineers Luis Moya Ydígoras and Ramón Aguinaga, it is a complex feat of engineering that can hold more than 58,000 cubic metres of water. It is now home to the Canal de Isabel II Art Room.

The tower, designed along the lines of a Roman cistern, is polyhedral in shape, with twelve sides, and right at the top is the water tank. Its elevation is made up of twelve buttresses that support it and help it sustain the huge weight it had when the tank was filled with water.

On the exterior, the building has an exposed brick facade, adorned on the Bravo Murillo side with a late Romantic classicist style fountain with a representation of the River Lozoya sculpted by Sabino de Medina, flanked by allegories about Agriculture and Industry, by sculptors Andrés Rodríguez and José Pagnucci, respectively. This work was made to commemorate the arrival of waters from the River Lozoya to Madrid.