my sink pipes are copper---could I assume the pipes under the house are copper too?
Never assume you know the old saying
I don't think so. I've lived in two old houses that had copper inside but iron pipes below.
Unlikely, unless the place was extensively rebuilt and remodeled - that happens, but not commonly. If you have plaster walls, not modern drywall, and if you have a fuse box, not a modern breaker panel, very unlikely. Take a look everywhere, not just the kitchen, for the pipes.If there was a major water leak and you had to shut off the main water valve inside, where would that be? Good thing to know itself, and, for this, a good place to start.
