The water on the toilet tank is actually condensation, caused by cold water chilling the tank, which in turn draws moisture from the warm bathroom air. To stop this, you can purchase a tempering valve that allows you to mix a small amount of warm water with that going into the toilet tank. Or there is a tank insulation kit now available to insulate the inside of your tank.
Need help installing a tempering valve?
Give Watters Plumbing a call at 920-204-7517 and we can help you out.