Symptoms
- Water droplets form on the outside of the tank
- Puddle forms on the floor even though nothing is leaking
- Worse in summer or humid weather
- Tank feels cold to the touch
Likely causes
- CommonCold tank water meeting warm humid airThe tank surface cools below the room's dew point, causing moisture from the air to condense on it.
- CommonHigh bathroom humidityPoor ventilation from showers or humid climates increases how much condensation forms.
- PossibleVery cold incoming water supplyWater straight from an underground line can be noticeably colder than the room, worsening sweating.
What to do
- Confirm it's condensation and not a leak by drying the tank completely and watching where moisture reappears first.
- Improve bathroom ventilation by running the exhaust fan during and after showers.
- Install a toilet tank liner kit, which adds insulation inside the tank to reduce the temperature difference.
- Consider a tank insulation blanket or foam kit sized for your toilet model as an alternative.
- Install an anti-sweat (tempering) valve if condensation is a persistent problem, which mixes in a little warm water.
- Wipe up condensation regularly and keep a towel or mat nearby to prevent floor damage in the meantime.
Tools and parts
- Towel
- Tank liner or insulation kit
Toilet tank insulation liner kitSearch: “toilet tank condensation liner kit”
When to call a pro
Call a plumber to install an anti-sweat valve if ventilation and a tank liner don't solve ongoing condensation and floor damage.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.