How do you know if water running through cast iron pipe?

You can tell if water is running through a cast iron pipe by listening for the sound of flowing water, which often produces a distinct gurgling or rushing noise. Additionally, you might notice vibrations or a slight hum in the pipe if water is actively flowing. If there are visible signs of moisture or leaks around the pipe, that may also indicate water movement. Finally, using a flow meter can provide a definitive measurement of water flow through the pipe.