noun
main shutoff valve; stopcock
Refers to the main valve that controls the flow of gas or water into a building. Often used in contexts of turning off the supply for safety or maintenance.
地震の後は、まずガスの元栓を閉めてください。
After an earthquake, please first turn off the main gas valve.
長期間家を空けるときは、水道の元栓を閉めておいたほうがいい。
When you're away from home for a long time, it's better to shut off the main water valve.