Mains water leak under the kitchen sink. Chaffing by the chipboard shelf over 30 years had eventually punctured the 15mm copper pipe to the cold tap. While in there noticed the screw for the electricity supply earth bond was laying on the shelf and the earth wire dangling in mid space ,ie not bonded, the bonding pipe clamp was perfectly secure. So was it flexing of the sink , every time of using the taps, caused the leak and undoing of that screw or something like waterhammer, not ever heard any water hammer though.