A constantly running toilet can waste a significant amount of water, depending on the cause and flow rate. Many issues are straightforward, but an overflowing tank or a problem that persists after simple checks should be addressed promptly.
Start with overflow protection
If water is rising toward the top of the tank or the toilet may overflow, turn the shutoff valve behind the toilet clockwise until the water stops. This gives you time to assess the issue without adding water damage.
Check the water level and float
If the tank water level is above the overflow tube, water may be continuously flowing into the bowl. On many toilets, the float can be adjusted using the manufacturer’s instructions so the fill level sits below the top of the overflow tube.
Test the flapper
The flapper is the rubber seal at the bottom of the tank. A worn, warped, or mineral-coated flapper can let water leak from the tank to the bowl. Add a few drops of food coloring to the tank; if color appears in the bowl without flushing, the flapper or another tank-to-bowl seal may be leaking. Replacement cost and installation time vary by toilet model and part.
Understand the fill valve
If the toilet refills briefly every so often when no one has flushed, a leaking flapper or another tank-to-bowl leak is often the cause. A failing fill valve can also cause overfilling or fail to shut off properly. Check the flapper first, then follow the toilet manufacturer’s guidance or seek help with the fill valve.
If the toilet still runs after these checks, request toilet repair service to have the flush valve, overflow tube, and other components evaluated.