Furna de Água is a cave in Angra do Heroísmo, on the island of Terceira in the Azores, Portugal. It was created about two thousand years ago from a lava tube of volcanic origin, and it is 560 metres long. Due to the presence of several springs within the cave, Furna de Água is one of the main sources of fresh water on the island. Although it has been known since 1838 (and perhaps earlier), Furna de Água has only been used as a public water supply since 1953.