The Gibeon Water Systems.
1. Pre-10th century B.C. “pool”
2. Stepped shaft to water table
3. Chamber at water table
4. City wall constructed in 12th–10th centuries B.C.
5. Spring
6. Feeder tunnel to increase flow of spring to water chamber
7. Water chamber
8. Outside entrance to water chamber
9. Stepped (or sloping) tunnel from inside city to water chamber
Gibeon—The earliest of three water systems was the pool, a large cistern which stored rain water (1). The pool was carved from solid rock some time before the 10th century B.C. During the long rainless summers this cistern probably stored an inadequate amount of water for the city.
The Gibeonites then constructed a second system to increase their water supply. This system consisted of a stepped sloping tunnel (9) leading from just inside the city wall to a water chamber (7) outside the city at the base of the hill. In order to avoid the pool, the upper portion of the stepped tunnel abruptly turned 90 degrees, flush with the city wall after it passed under it. The water chamber at the lower end of the stepped tunnel was filled by fresh water from the spring (5) under the hill. The water flowed from the spring to the water chamber through a feeder tunnel (6) which increased the flow.
After completing this feeder channel, the Gibeonite engineers may have realized that they had tunneled to a point almost directly under their cistern pool. They then decided to dig below the cistern pool to the level of the spring (2), intending to dig a tunnel to the spring. Before reaching the spring they hit the water table, thus discovering an abundant source of water without tunneling to the spring. There they carved out a kidney shaped water chamber (3).