Why toilet tank losing water?

There is a rubber seal between the tank of the toilet and the bowl. This rubber seal is not sealing. It could be torn, something stuck in there, or just old and stiff and doesn’t seal correctly any more.

First, take the lid off and look at the bottom where the water drains from the tank into the bowl & be sure nothing is getting caught in that rubber seal. If so, remove it and problem solved. If not, keep reading.

To make sure it’s leaking into the toilet bowl, you can put some food coloring in the tank, then see if the toilet bowl water turns that color.

Either way, you’ll need to replace that seal. You’ll be best served if you just replace the “guts” of the toilet. This can be found at any hardware store in the plumbing section. It’s easy for anyone to do as long as you’re able to follow directions.