And do not forget good old part Pof the building regs
remember water and electricity do not mix very well to say the least
Do you know what you are doing? what is the size shower you are fitting? what is the csa of the cable you are using is it big enough, is there a RCD fitted does it work in less than 200ms, What is the Zs earth loop value like, is there sufficient bonding????
lots of questions which are all about your safety