The water supplies go off. Mike tells Liz his experience with the "winking" keyhole and from this she decides that Martyn must have bugged the main room but not the bathroom area where Mike and Liz have been talking.
The water supply is cut off. Mike shares his encounter with a "glancing" keyhole, leading Liz to conclude that Martyn likely installed a listening device in the main room but not in the bathroom where Mike and Liz were conversing.