How come ZamZam water in Mecca never runs out? It is located in the middle of a dry desert in Mecca and the astonishing thing is all wells around Mecca dried out except this one!

So how can a small well, with a diameter of about 1.46 meter to 2.66 meter, and the depth of about 30 meters quench the thirst of billions of people from all over the world throughout centuries?
The Zamzam Well is located in the Wadi Ibrahim. It accesses water from the wadi alluvium and from the bedrock. 


  Water in the well comes from absorbed rainfall in the Wadi Ibrahim, as well as run-off from the local hills. Since the area has become more and more settled, water from absorbed rainfall on the Wadi Ibrahim has decreased.