What you do, is to supplementary-bond each metalic pipe that enters the bathroom to the earthwire of each electrical circuit that enters the bathroom. If you do this when they come in, you don't need to bond that same pipe again (e.g. at each tap, or each light fitting), because there is nothing in the bathroom that can add a voltage to them.
You can do the bonding in an adjacent airing cuboard if the pipes go through there into the bathroom.
There is a useful download document you will find if you do a "search" on +Supplementary +bonding.
The question is a very common one.
If you have an old house with iron soil pipe of lead waste pipe, you must bond them too.
You can generally connect to the Lighting circuit at the ceiling switch, and run the G&Y down with the pipes. If you have a shaver socket on a different circuit, or an immersion heater or wall heater, you will have to bond to those circuits as well. The bonding clamps must be accessible for inspection and maintenance so don't bury them in plaster, or tile over them.
