It's quite possible that you both have a shared water supply from the street and if it is, it's likely a small bore lead pipe.
Not uncommon in the past for former local authority properties or properties built for a single landlord.
Old...
Hi,
We moved to a 1950s semi in Dec last year. We’ve noticed over the months that’s the electric shower will randomly have episodes whereby it starts to go hot and cold for no apparent reason. Same has just happened now and I thought...