Nobody was on the tower - the Dome thing at the top not big enough for a shooter to hide behind either.
There is plenty of room on that tower—even two people could stand there comfortably—along with maintenance gear.
There was a ladder inside the tower that led all the way to the top. It was designed so maintenance could be done from the top.
It was a reasonable standard water tower design.
This is a different water tower in Indiana but similar design—that shows all the features:
https://www.dronegenuity.com/projects/elkhart-water-tower-in/