[EN] At the fourth century Christian monasticism leaves the anchoritic lifestyle begining a new monastic organization. These religious communities not only shows an architecture of monastic life, but it also highlights a whole hydraulic network that sometimes is reflected in valuable drawings.From the first graphic document of Saint-Gall until the parchment of the Corb River, photographed exclusively from the Vallbona monastery registry, this study shows the importance that the graphical representation of the water network has had all along the history.Thanks to these graphic documents nowadays we can know about important historical documentation such as irrigation rights, property boundaries, paths of ditches, water pipes, building systems, etc.. rising to become the only witnesses of an underground architecture, in many cases already disappeared.