The desert has water, it is just that you can't see it and most of the time you can't get to it. But sometimes you can both see and get at it.
The well. It is a collapsed sinkhole formed when underground waterflows eroded the overlying strata, forming a cavity. When the cavity grew big enough to not be able to support the top, it fell down, leaving a water-filled hole in the middle of the desert.
The hole seen from the opposite rim. Note the houses built into the wall - it was a popular way among the people living here of building houses that were well-protected and warm.