Compare and contrast the photo above with another one from the early days after the Water Tower was built below.
Notice that in the upper picture the current cupola of the High Bridge Water Tower is not yet installed as shown in the lower picture. The pumping station and smoke stack are also clearly visible in both pictures. In the lower picture you can also see the reservoir behind the Water Tower. The Water Tower was authorized for construction in 1863, but was not completed until 1872, so the picture with the partial completion of the Water Tower had to be taken before the completion date of 1872.
In this last picture from 1863 you can see the construction of the third tube on the Aqueduct when it was expanded. While the other two pictures were shot facing Manhattan, this was shot from the Manhattan side facing toward the Bronx. At this time, in 1863, the construction of the Water Tower had not been started yet. The construction of the pedestrian walkway was also not started either.
For more information on the High Bridge Aqueduct Water Tower see our post from 2013