As related to BS7671.

If a sub-panel happens to be part way along the same route that the main equipotential bonding cable must go to the incoming water supply, is there anything to prevent that condcutor being shared as the earth to that sub-panel, assuming that it can be fed through and connected to the earth bar in the panel without being cut?

I can't see anything against doing this, but it's not something I ever recall coming across before.