There should be a valve on the main feed into your house. This is
often under the kitchen sink or in a bathroom closet. There is also a
main shutoff valve at the street under a lid, usually. Make sure
it works!
You and anyone else living in your house should know where the
stopcock is and how to turn it off.
Somewhere outside your house there will also be a main stopcock.
This will almost certainly be below a small trap-hatch somewhere on
the street or road outside. However, if a new drive surface or road
has been laid, the hatch may become concealed. Make sure you know
where it is, how to get to it, and how to operate it.
You should also know that where the hot and cold service valves
are. Make sure they work.
If you are unsure of the whereabouts of these valves or stopcock,
ask your plumber next time he or she visits.