The Running Toilet and the Silent Leak

Ten minutes and a few drops of food colouring settle the question.

EPA WaterSense describes the standard check: put a few drops of food colouring in the tank, wait about ten minutes without flushing, and look in the bowl. Colour in the bowl means water is passing the flapper, which is a leak. Flush immediately afterwards so the dye does not stain the tank.

Continuous refilling and periodic short bursts fail differently.

Water trickling into the bowl with the tank never quite filling points at the flapper seal. A tank that refills briefly every few minutes with no visible flow is the same leak, refilled in bursts. Water running into the overflow tube instead means the fill valve or float has the level set too high, so the tank is overfilling into the drain by design.

Most tanks mark the intended line.

Adjust the float so the water stops roughly an inch below the top of the overflow tube, or at the manufacturer line moulded into the tank. If the level is correct and the bowl still takes water, replace the flapper with the part specified for that model; a mismatched universal flapper often seats poorly and recreates the leak.

Household leaks are measured in thousands of gallons a year.

EPA WaterSense estimates that household leaks waste more than 10,000 gallons per year in an average home, and that fixing easily corrected leaks can save around ten percent on water bills. A toilet is the most common single contributor because nothing drips on the floor to announce it.

A dye test that stays clean sends you to the meter.

If the dye test is clean and the bill is still high, the leak is elsewhere: an irrigation zone, a water heater relief line, a supply line inside a wall, or a service line before the house. The meter test isolates those without guesswork, and a leak that soaks structure or appears at a joint you cannot reach belongs with a licensed plumber.