The second man's equipment somehow became suspended in the tank, which had been drained for maintenance. The trapped man was wearing a work harness and had fallen only part of the way, said Montgomery County Coroner Walter Hofman.
The extent of the man's injuries were not yet known.
An investigator from the U.S. Occupational Safety and Health Administration was on his way to the accident scene, the coroner said.
The second man was pulled from the tower about 2:20 p.m. after an intense rescue effort. Lower Providence Police and Fire Departments, along with crews from King of Prussia and Plymouth Township, were at the scene. At least a dozen emergency response vehicles also were present.
The three employees worked for Corrision Control Corp., of Pedricktown, N.J.
Audubon Water Company, which has an office in Norristown, serves parts of Lower Providence Township.
The tank stands high as nearby treetops in the surrounding residential neighborhood on Featherbed Lane.
Contact Aubrey Whelan at 610-313-8112, at email@example.com or follow @aubreyjwhelan on Twitter.