## 1 Introduction
Although they recognised their relevance within cultural, industrial and maritime landscapes, both urban and rural, they did not generally cover the territorial extent of the system, only looking at different elements in isolation (dams, tanks, pumping stations, water treatment plants, etc.) rather than the whole system. The best-known example of heritage recognition of a water supply system as a whole is the Old Croton Aqueduct in New York (1837-1842). It was designated a National Historic Landmark in 1992 from the Croton dam until the touchdown of the High Bridge in Manhattan (41.8 km). It also has several individual structures listed individually on the New York State Register of Historic Places [32] (pp. 89-93). However, its recognition as a landmark of civil engineering came once it was no longer used due to insufficient supply (1955) and was replaced by the New Croton Aqueduct, which tripled its dimensions. In 1968, it became the Old Croton Aqueduct State Historic Park, thus adding a new recreational and cultural use to its heritage and symbolic dimension. Another similar case of heritage recognition is the Lisbon water supply system (1731-1799). It was designated as a National Monument in 1910 and included in the UNESCO \"Tentative List\". It remained in service until 1968. Its most iconic elements, namely, the Aguas Livres aqueduct bridge (1748), the Mae d'Agua das Amoreiras cistern (1746), the Patriarchal Reservoir (1864) and the Barbadinhos pumping station (1880), are managed by the Water Museum, an institution responsible for research and dissemination of water resources [34]. Fortunately, in both cases, functional obsolescence has not led to their abandonment, but rather, these public works have acquired new values and meaning not only as engineering landmarks but also as identity elements of the landscape that they form. The management of an operational supply system as a historical resource, as in the case of Canal de Isabel II, is more complicated, as utility usually takes preference over heritage, historical, cultural and landscape values. The study forms part of the research project \"Analysis and definition of territorial scale strategies to characterise, restore and heighten esteem for the public works heritage\" [35]. A number of sources were used for this research: academic research material, UNESCO documents, media reports and field work on several sections of Canal de Isabel II. Under the Section 2, there is an analysis of the historic construction of Canal de Isabel II and its subsequent development. We identified the \"visible\" parts of the system, its structures and its constructions that demonstrate the values described by [PERSON] [32]. We address a management system that allows the supply network to be run alongside the use or transformation of its cultural elements. Under the Section 3, we emphasise the overall value of the linear public works, their interest as networks connecting different places and actions, and their value as cultural heritage beyond their practical use. In Canal de Isabel II, we highlight newly acquired values and the new uses of some of its components despite the obsolescence of their original function. The final Discussion resumes the matter of the territorial nature of public works, the importance of discipline over the landscape in order to understand and value it, opportunities and new uses, concluding with the importance of considering their value as a whole.