If your house is humid and the water that is coming into your toilet is cold it can get condensation. This water will drop off of your tank onto the floor. This could be your mystery leak. This occurs many many times in the winter especially in homes that have humidifiers. As the water in the tank warms up the condensation stops but you are left with a puddle of water on the floor. If you are looking everywhere for that elusive leak this might just be your answer.
There are remedies to this which can be a little bit tricky but it is far better than risking damage to your floor. Even laying a thick towel down is a big plus but, I had this happen to me and it ruined my floor to the point I had to replace it. The tank can be insulated. After draining the tank and shutting off the water at the shutoff valve, remove the tank lid, flush the toilet and hold open the tank stopper or flapper to drain as much water as possible. Use a large sponge to remove the rest. Cut appropriate-size sections of foam from a tank-insulating kit. Spread adhesive on the tank walls to adhere the foam. I also suggest reading the directions.
The next solution involves hiring a plumber for their services with installing a tempering valve.
