This would depend on many factors.
The original idea was to connect all metal parts in a bathroom together so they will all be at the same voltage.
As plastic pipes started to be used it was found this no longer was the safest method and as an alternative all electrical items in a bathroom must be supplied through an RCD.
So your wire may be left over from a previous system. It may need connecting to another pipe. It may need connecting to an electrical point like a shower or towel radiator etc.
It is impossible to give any real answer here as so many options.
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