Medieval Madrid was a bustling urban center that needed large supplies of water. The Magerit or place of waters, according to its Muslim founders, was supplied with "water trips". It is a system of underground galleries to carry water from the headwaters of the rivers to the 54 fountains in the city. There it was collected by a thousand watermen who sold the liquid from the houses. The system worked until the middle of the 19th century. The population multiplied disproportionately, surpassing 200,000 inhabitants in the reign of Isabel II, and the network of "water trips" was insufficient to supply the people of Madrid. In addition, the old and dilapidated canals built a thousand years before were a source of infections and epidemics. The historical tour of the Canal de Isabel II covers the facilities of the Pontón de la Oliva, with information panels on the history of the dam, architectural details, surrounding buildings, conduction systems and other curiosities of the first historical milestone that allowed the people of Madrid to have access to drinking water. The Canal de Isabel II has 14 reservoirs in the valleys of the Lozoya, Jarama, Alberche, Guadalix, Sorbe and Manzanares rivers.