The same natural water sources which enabled people to settle the island of Thera in the 8th century BC, are still visible today on the hill of Mesa Vouno. An extensive infrastructure for the exploitation of rainwaters was established in the city of Ancient Thera on Mesa Vouno, which is striking for the quality of its construction as well as the inventiveness of its builders. Rainwater followed the course that was prescribed for its storage from the flat rooftops to underground cisterns. The water on the roof of the temple of Apollo Karneios followed a comparable route, the study of which answered many questions regarding a false – as it turned out – reconstruction of the temple plan. The above study is completed by the production of an axonometric visual reconstruction of the temple.