The Gihon Spring was the main source of water for the City of David, the original site of Jerusalem. One of the world's major intermittent springs—and a reliable water source that made human settlement possible in ancient Jerusalem—the spring was not only used for drinking water, but also initially for irrigation of gardens in the adjacent Kidron Valley which provided a food source for the ancient settlement. The spring, being intermittent, required the excavation of the Pool of Siloam which stored the large amount of water needed for the town when the spring was not flowing.

• http://en.wikipedia.org/wiki/Gihon Spring