Just out of interest. I removed an old cylinder from a house built in
1975 or 1976. Under the copper cylinder a thick earth wire was soldered to the bottom. This went to the hot water draw off pipe where it was clamped. Then the wire went to the cylinder cold feed pipe where this was clamped. This was some sort of bonding. The cylidner had two immersions, one top one bottom, of which only one at a time could be be on because of a sink/full bath controller.I thought this bonding was not required in those days, so why do it? The soldered wire to the cylinder looked over the top. All this was from when the place was new, not fitted after.