The British System- When the British arrived, the Hasmonean water aqueducts were already inefficient, whereas the water needs of the city were great. As a preliminary solution, the British fixed up part of the aqueduct from the southern side, changed the pipes to iron pipes (as opposed to clay or stone) and added some pipes of their own and, soon enough, an abundance of water was running through the pipes in Jerusalem. The British also added pumps which prevented the need to create tunnels or turns around the mountain.
However, the British knew that all of this was not sufficient and they therefore also pumped water from Ein Mavo, which is a spring in Wadi Qelt on the eastern side of the city. They brought the water to Jerusalem and this water source of Ein Mavo served Jerusalem until the Six Day War (1967).
However, the water from Ein Mavo were not sufficient and, as a result, the beginning of a water supply system from the direction of Rosh HaAyin started emerging, at a distance of 60 km from Jerusalem. Along the pipe are two incredibly powerful pumps (that can be seen when travelling on Route 1 to Jerusalem) and also accumulation pools at the entrance to the city. This system, with certain changes, still works today.