I have a butchered bathroom that I'm trying to restore to its original layout. The picture attached is of the wall between the other, functioning bathroom and the project bathroom. You'll see supply lines coming up on the left and right. The question is: Why is there 3/4" copper connecting the two? Is it necessary? It would be FAR easier to re-frame this wall if I could safely remove it.

Why is there 3/4" copper connecting the two?
Code calls for not over three fixtures to be supplied by a 1/2" supply. Since I don't know how many fixtures those 3/4" mains are feeding I can't answer your question. Regards, Tom

On the left there is a functioning sink, functioning toilet, and future shower. On the right there is a functioning shower/tub and a future toilet. The sink for the project bathroom is around the corner and supplied by a line on an exterior wall.

Does that help?

OK! The cold water main must remain 3/4" as it continues on to pick up three fixtures.
However, the hot water main can be reduced down to 1/2" providing when reduced it doesn't supply more then three fixtures. Good luck, Tom