Often when we think of a lightning transient, the idea is that the lightning strikes a power line and propagates through the hot/neutral or 3 wires of 3-phase system. There is also induced current transients.
However, I wonder to what extent lightning can affect the ground system. Most houses where I live are grounded to the water pipe in the house, so I would guess that if the lightning hit say a bridge with a water main on it, it could affect equipment attached to that water line. One article on lightning surges had the paragraph:
Lightning ground current flow results when a strike that discharges to
the earth couples into common ground impedance paths, causing voltage
differential across the ground grid and between ground-neutral or
ground-line circuits. In short, the reference ground (supposedly zero
voltage) is elevated a few milliseconds, therefore creating a large
voltage difference between ground and the incoming power and/or data
lines.
To what extent, if any, does lightning affect ground systems which use water pipes?
Best Answer
There is one cardinal mistake. The water pipe may not be used as ground, rather a water pipe has to be grounded. Grounding the pipe provides safety to the user if some device, for example boiler malfunctions so that you don't get electrocuted in bath.
It is forrbiden to attach other devices to the pipe to serve as ground point.
When the lightning strikes a grounded object, the current passes through and the entire grounding potential becomes V=I*R_ground. It is self explanatory that having good ground makes this voltage very small.