Petra’s vital water supply was provided in two ways: by building water conduits to serve the city area, and by storing rainwater in cisterns. The most important water source was the Moses Spring in the Wadi Musa. The water reached the city via two conduits that ran through the Siq – the narrow rocky gorge.
The northern water conduit was a pressurised earthenware pipeline, some sections of which were embedded in an older channel. On the south side, a spring water conduit covered with sandstone slabs ran along the road at a height of one and a half metres, or five feet.
The Khubtha pipeline brought water from the Moses spring to Ramla. On its way into the city, it ran across three arched bridges, only one of which has survived. The pipeline fed a large reservoir northeast of the Palace Tomb. Excess water was channelled into a large collecting basin and supplied mills and other businesses.
A great many cisterns helped to boost the city's water supply. Rainwater first flowed through channels in the rocks into collecting basins, where sand and impurities settled. Then the water was channelled into cisterns. The cisterns were plastered with mortar and covered with stone slabs to prevent algal growth.
In front of the entrance to the Siq, a dam measuring 12.8 metres or 42 feet protected the city from flooding during the winter rains, when water from the Wadi Musa would have flowed into the narrow rocky gorge. The water was diverted through a 90-metre tunnel. Additional dams sealed off the side valleys.
