How to check a toilet for a silent leak

Last reviewed November 1, 2026 by Jordan Reeves

Put a few drops of food coloring in the toilet tank, wait 10 minutes without flushing, and look in the bowl. If the color has reached the bowl, the tank is leaking. EPA suggests checking at least once a year.

How often: At least once a year, according to EPA.

Steps

Lift the tank lid off with both hands and set it on a towel on the floor. It's heavy and breaks easily.
Add a few drops of food coloring to the tank. Don't flush.
Wait 10 minutes, then look in the bowl.
Color in the bowl means the tank is leaking, often at the flapper.
Flush right away to clear the coloring, so it doesn't stain. Put the lid back.

Stop and call

Call a plumber: if color reaches the bowl. Thrively leaves work inside the tank and its water supply to a plumber, and it's usually a quick repair.

Why it matters

EPA estimates that a small leak from a worn flapper can waste about 860 gallons a month, and a badly misaligned flapper about 8,600 gallons a month.
EPA says the average household's leaks can waste more than 9,300 gallons a year.

Sources

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Thrively says no: call a licensed plumber. Rheem and A.O. Smith both call for flushing about once a year, but the job means draining very hot water around gas or electrical parts, so we don't publish steps for it.

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