About Toilet-Tank Sweating

Toilet tanks sweat when the water inside the tank is cooler than the temperature of the air in the room. Condensation appears on the exterior of the tank. This can happen sporadically, such as after you shower or only in the summer, or it can be an ongoing problem.
The condensation can drip onto your floors, causing problems that range from puddles to mold and mildew that leave an unpleasant smell and ruin your bathroom carpeting.
There are, however, certain solutions to toilet-tank sweating.

Identification

If your toilet tank is sweating you will know. It is easy to identify because you will see drops of condensation on the outside of the tank, and you may notice that you have puddles of water that accumulate on the floor.
You will need to find out if the sweating occurs only after a shower or bath, when the hot water and steam heat your small bathroom up and cause a considerable difference between the temperature of the water on the inside of the tank and the outside air. If you identify this as the problem, you might simply need to use more ventilation in your bathroom. Make sure to open some windows and always turn on your exhaust fan.
If your tank is noticeably sweating at all times of day, you will have to look for a solution outside of just running the exhaust fan.

Prevention/Solution

If your tank is sweating at all times, you can stop it by installing a toilet-tank liner.
Toilet-tank liners can be purchased at your local hardware store or at any big box retailer. To install your toilet-tank liner, first drain the toilet, then further dry the inside of your tank using a hair dryer to ensure the liner will stick once placed in the tank. Fit the foam into the tank to size it. Cut the foam if necessary. Once the foam is sized, glue the foam into the tank and allow it to sit for eight hours. Refill your tank and your sweating problem should be resolved.

Considerations

Your tank may be sweating because your flapper valve is leaking. When the flapper valve leaks you experience a constant stream of water running into your tank. This will raise your water bills and causes the water in your tank to remain cold. The water is never given the chance to warm up to room temperature because it is constantly flowing.
To see if the problem is your flapper, drop food coloring in your tank and let it rest for two hours. When you check on your toilet, if you notice that the water in the bowl has turned the same color as the food coloring you have a leak and you need to replace your flapper.

Misconceptions

Some people believe that putting a decorative toilet-tank cover on will solve the problem. It is true that you will not notice the condensation and it will keep your toilet tank warmer, but it does not solve the problem of a sweating toilet tank. It is just a cosmetic coverup. You need to get to the root of the problem and identify the issue.

Expert Insight

Consult an expert if you are still experiencing problems with your toilet tank after trying several home remedies. An expert will probably recommend installing a mixer to the pipe leading to the tank. This will enable you to adjust the temperature of the water that flows into the tank. You will be able to add a stream of hot water, which will prevent sweating and ensure that your tank is always at room temperature.