The present study is based on periodic field work in the years following 2000 CE in the privately owned areas surrounding the public world-famous Unesco-site of Villa Adriana. The subject of the study is the reconstruction of the external water supply for Villa Adriana: from where came the water and how was it conducted to its destination? This subject is crucial for the understanding of the famous Imperial residence, a question asked by probably every visitor to Hadrian’s architectural masterpiece. This question has also been asked, or actually just touched, several times by scholars since at least the 18th century, but never answered systematically and with satisfactory results. In fact, the question how the Villa was supplied with its remarkable and necessary amount of water has remained quite open until today. The study identifies five aqueducts in the area south of Villa Adriana, from either historic research or the few remains still present. Two of them were identified as millraces, feeding waterwheels and grain-mills. One was accepted as the correct answer to the question. The study recognises the supply system of the imperial Villa as a branch aqueduct from the public urban Roman aqueduct Anio vetus. It had already for generations supplied the republican villa situated in the later Hadrianic project area. Hadrian just had to extend it by a new branch from Anio novus. In appendices, not loading the treatment of the main subject but completing it, are treated several…