Sorry I didn't clarify. We have our own backyard which is separated with by a fence. So shouldn't his HWS be on his side of the fence? It is also connected to a GPO which I am not certain who it belongs to. And when he requires maintenance on it, he would have to come through my apartment?

We live in an apartment, ground floor unit with a backyard. I have my own hot water service on the external wall and next to it is my neighbours. It was built like this and it is in the architectural drawings. Is this compliant with the building regulations?