Chapter 15, Problem 78P

A plumber conies to your ancient apartment building where you have a part-time job as caretaker. He’s checking the hot-water heating system, and notes that the water pressure in the basement is 18 psi. He asks, “How high is the building?” “Three stories, each about 11 feet,” you reply. “OK, about 33 feet,” he says, pausing to do some calculations in his head. “The pressure is fine,” he declares. On what basis did he come to that conclusion?