This third container can be seen to be filled to a level above that of the connecting tubes.



Water can pass through the joining tubes in any direction to equalise the levels in the upright tubes.

This is similar to an active corrosion cell in which any energy available due to the reaction at the anode is able to pass through the electrolyte to the cathode.



We need to be able to measure if the water is flowing but have no way of doing this without altering the amount of water flowing!