Toilet shuts off, but later the tank has lost water and refills. The lost water doesn't appear to be leaking out. What can I do? It wastes lots of water.

Hi Scienceteacher...

Sounds like you have a bad toilet flapper there. To confirm a bad flapper take some food coloring and drip in about 15 drops of a dark food coloring into the toilet TANK.

Let that sit for an hour or so and if the coloring shows up in the toilet BOWL you know the flapper is bad and needs to be replaced.

If the flapper is bad, turn the toilet shutoff off and remove the flapper and take it to a local home supply store and replace it with the best fit replacement flapper.

If you have issues beyond that, let me know, OK?

Mark