A hydrological edifice. As explained in A practical treatise on hydraulic and water-supply engineering: relating to the hydrology, hydrodynamics, and practical construction of water works, in North America, (which I found on archive.org):
The stand-pipes as generally used, serve as partial substitutes for relief-valves combined or acting in conjunction with tall and capacious air-chambers. The surface of the water in the stand-pipes vibrates up and down according to the rate of delivery into them from the pumps, and the rate of draught, if the main over which they are placed is connected with the distribution. In northern cities it is necessary that they be housed and protected from frost.
The Boston Highlands Stand-pipe (page 161) stands upon an eminence 158 feet above tide, is of wrought-iron, and is 80 feet high, and 5 feet interior diameter. It is inclosed in a masonry tower.
Looks a bit like a fortification, and a bit like a church steeple. But it’s plumbing for a city.