Most toilets have a small shutoff valve on the wall or floor behind the bowl. To stop a tank leak or prepare for service, close it gently and then flush to confirm the tank does not refill. Do not force an old valve that is seized.
Find the valve on the line feeding the tank
Follow the supply line from the bottom of the tank toward the wall or floor. The small valve at that point normally controls only the toilet.
Close it by hand without excessive leverage
A wheel valve usually turns clockwise to close, while a quarter-turn lever moves until it is crosswise to the pipe. If it is corroded or will not move, do not force it because the valve can break and create a larger leak.
Flush to confirm water has stopped
The tank should empty and not refill. If water continues entering strongly, the valve did not close or is not the right one; during a serious leak, use the home’s main shutoff.
Repair a shutoff that does not seal before the next emergency
A valve that leaks at the stem or continues passing water may need replacement. Servicing it requires shutting off the main supply and controlling residual water, so a plumber may be the better choice.
Sources
- U.S. Environmental Protection Agency WaterSense — Home Maintenance — Household maintenance related to water, leaks, toilets, pressure, and efficient use.