Was modern plumbing added later to pre-plumbed homes in Europe?

You know how there are all those old row type houses in Europe, in places like Italy, with the cobblestone lined paths. I think some of them were built before modern plumbing, say 400-ish years ago.

As far as water and sewerage, were those systems added to these homes after modern plumbing was invented? Or just never added? How did they do it? They dug up those old stone streets to install the waste pipes and water lines?

Just curious