How To Fix Condensation On A Toilet Tank | Simple Solutions

Have you ever gone into your bathroom in the morning to find condensation on the toilet tank dripping down onto the floor? It can be quite an annoyance and may cause deeper, longer-term issues with your flooring.

So, what exactly is going on and how can you fix it?

In this post, I’ll explain why you get condensation on a toilet tank and how you can stop it. As well as answer some popular questions about the topic.

Let’s dive in!

Why is there condensation on my toilet tank?

Toilet tanks are notorious for sweating or collecting condensation on hot summer days. Why does it happen? The good news is that your toilet is not broken or defective. This is all about the science of weather.

The water inside your toilet tank typically enters the house at a temperature of around 10 to 12 C. In the middle of the summer, the air in your home will be about 24 to 27 C with a dew point of about 18 C.

With cold water in the tank, the toilet’s ceramic becomes colder and can drop below the dew point. When that happens, moisture in the warm air will collect on the toilet tank and produce condensation.

Toilet tank with condensation, toilet sweating
Toilet tank with condensation

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How can I stop condensation on my toilet Cistern?

There are a few reasonably simple upgrades available to fix this recurring problem.

Install a New Toilet

A sweating toilet is most commonly associated with old toilets in older homes. New toilets come with an insulated tank that will not sweat as often as the older models. Yes, even the £150 toilet sold in the bargain section of the home improvement store includes an insulated tank.

You can do the switch yourself with the help of a buddy and some DIY experience. You might pay a pro around £200 to get it done.

Add a Toilet Tank Insulation Kit

For about £20 you can pick up a roll of toilet insulation at the hardware store.

You will need to shut off the water and drain the tank. Remember, the water in the tank is just as clean as the water coming out of your taps. The thin insulation is cut to fit your tank and sticks to the porcelain. The job takes a couple of hours, and you eliminate those pesky puddles in the bathroom.

Add a Warm Water Mixer Valve

A permanent fix for condensation on your toilet is to raise the temperature of the water in the tank. Your plumber can add a mixing valve that introduces a little hot water during the refill cycle. Now that the tank water is the same temperature as the room, no water will collect on the outside of the tank even on high-humidity days.

The valve costs less than £20, but you could spend up to £500 on a plumber and wall repair. In most homes, the technician will need to open up the wall and run a new hot water pipe to the toilet. This is a great solution if you are doing a bathroom renovation.

Run an Air Conditioner or Dehumidifier in the Bathroom

Your home’s A/C will help to lower the dew point in the bathroom, which will reduce the amount of sweat you see on the toilet. Another option is a dehumidifier.

It does not cool the air, but it dries it out. This will also help to reduce the growth of mould in the bathroom. 

Toilet Tank Covers

Some people will recommend wrapping the tank in an absorbent cover. This provides some insulation between the cold tank and the warm air and runs about £20. They are available in decorative colours to match your towels and rugs.

However, it is more likely that the cover will stay damp, which may result in the growth of mould on the cover. If you wash the cover every week, it works. Otherwise, it is an imperfect solution.


Is my toilet leaking or is it condensation?

If water has beaded all around the tank and the bowl, but it stops at dry sections of porcelain, this is a good indicator of toilet condensation.

Whereas a leaking toilet will not have water on the exterior of the bowl or tank except at the point of a crack.

Toilets most commonly leak inside at the flapper valve. If your toilet is always running, you are more likely looking at an interior leak.

If you have water on the floor beneath the toilet, but no moisture on the surface of the toilet, and you notice a stale odour you may have a leak at the main drain seal.

What does it mean when a toilet sweats?

Your toilet is not broken. Sweat happens during hot and humid days in the summer or just after a lengthy steam shower. The toilet surface is much colder. Moisture beads on the surface of the toilet porcelain when the hot moist air hits the cold piece of sanitaryware.

The sweating toilet will dry up when the humidity in the bathroom and your neighbourhood drops to a more comfortable level.

Is toilet sweating normal?

Yes, toilet sweating happens during the humid summer months or maybe after you steamed up the bathroom. The toilet is not leaking.

The colder water in the tank cools down the porcelain. When the hot air hits it, beads of moisture collect on the surface.

Is toilet sweat unhealthy?

The condensation on your toilet tank is actually some of the cleanest water that you can find. If it has any bacteria, it comes from the surface of your toilet or the floor.

However, a puddle of water that sits on the floor by the toilet is much more likely to provide a place for germs to grow.

If you see sweat on the toilet, there is a good chance that mould is growing on other surfaces in the bathroom. A dry bathroom is a healthier bathroom.

Will caulking stop toilet sweat?

Adding silicone caulk around the base of the toilet will not stop your toilet from sweating. This only helps if you have a leak at the wax ring under the toilet–but it doesn’t fix the problem.

You really need to replace the wax seal or replace the toilet.

Final Thoughts…

There you have it! Now you know why your toilet has condensation forming on it and how to fix the problem.

For most, there can be a simple, quick and cost-effective fix to stop your toilet from sweating.


Michael R

Michael is a KBB designer from the UK. He's been designing and project managing new Kitchen, Bedroom and Bathroom installations for over eight years now, and before that, he was an electrician and part of a KBB fitting team. He created The Bathroom Blueprint in early 2020.