Venetian tanks.  “Venezia è in acqua e non ha acqua” (Venice is in the water and has no water): this famous quote by Marin Sanudo, an old diarist and invaluable witness of the life of the republic between the fifteenth and the sixteenth centuries, admirably summarizes the problems that the inhabitants of the islands in the lagoon had to deal with from the very beginnings to be able to live in that site, protected by its lagoons but very difficult to colonize. The hydraulic device that allowed the city to be born and to flourish over the centuries is the  filtration tank for the collection of rainwater, that, crowned by its wellhead, still adorns almost every venetian campo, as well as private courtyards of houses and palaces.A census of the nineteenth century, ordered by the municipal engineer Giuseppe Bianco, recorded about seven thousand tanks in the city, including external (located in campos and courtyards) and internal (located in the entrances of houses and buildings). While the external tank collects rainwater from the near rooftops and from the surface of the campo (or courtyard), the internal tank collects it from the roof of the buildings only, through an ingenious system of gutters and pipes inside the walls. This second type of tank, however, was invented much later in fact, there is no documentary sources on it before the early years of the fifteenth century, when the still evolving and growing city needed new spaces to expand and could no longer afford the large open areas (campos) that had characterized its organization up to that time. Another important distinction is that between public and private wells. Public wells were of course those located in the campos and in the public courts, but very often also those of the convents, which were made available to people during certain hours of the day. In fact the houses of the common people were not equipped with wells,  as they were too expensive products, unlike the patrician palaces.The wellhead was located in the inner courtyard (court) of the palaces, also the clientes of the owner usually had permission to draw water.(GIANIGHIAN PAVANINI)