Boiling water?

Question

What causes the rumbling sound you hear right before water begins to boil. Also what is the average temp that hotels set their water thermostat at?

Answer 1

The rumbling does not come from the water but from the kettle or pan that the water is in. As the water approaches boiling point the hyper-activity of the molcules transmit mechanical action to the container they are. This vibration on a stove or a heater creates the rumbling.

Most hotels set their water temperature at 130 - 140 degrees to prevent burns.