The "water tower" is the massive clump of rock just left of the center of the image. View looking west. This water tower is located on the south side of Laodicea very close to the stadium and to the bath/gymnasium.
Evidently water entered the city from the aqueduct coming from the south, was "pumped" up to this area, and into this structure This is actually a constructed structure – made out of individual blocks of stones and clay pipes. It seems that water was "pumped" up through the clay pipes and that it spilled out over the top, cascading down the sides of this structure — like a "bubbler." The constant flow of water left behind calcium deposits and thus the amorphous – almost solid – appearance of the structure.
For a view of the "interior" of the "water tower" Click Here.
For a map and brief description of the historical and biblical significance of Laodicea Click Here.