If you notice water dripping or pooling on the floor beneath the toilet tank (behind the toilet), the problem is likely caused by a leaking water connection or worn tank component. Toilet tank leaks usually occur at the water supply connection or internal seals inside the tank.
Most toilet tank leaks can be repaired easily by tightening connections or replacing inexpensive parts. Start by identifying where the water is coming from before attempting a repair.
Quick Answer
A toilet leaking from the tank is usually caused by loose supply line connections, worn tank bolts, or a failing flush valve gasket. Tightening fittings or replacing the affected parts typically stops the leak.
Common Signs of a Tank Leak
You may notice:
- Water pooling behind or beneath the toilet tank
- Drips forming under the tank
- Moisture around the tank bolts between the tank and bowl of a two-piece toilet
- Water running down the outside of the bowl from the tank
- Damp floor behind the toilet
If moisture forms evenly across the outside of the tank, the issue is probably condensation rather than a leak. See Toilet Sweats (Condensation on Tank).
Likely Causes
Most tank leaks are caused by one of these problems:
- Loose water supply connection
- Worn or damaged supply line
- Leaking tank-to-bowl bolts
- Failing flush valve gasket
- Cracked toilet tank
Identifying the exact location of the leak will help determine the correct repair.
Tools & Materials
You may need:
- Adjustable wrench
- Screwdriver
- Towels or sponge
- Replacement supply line
- Replacement tank bolts and washers
- Replacement flush valve gasket
- Rubber gloves
Step-by-Step: How to Fix a Toilet Tank Leak
1. Check the Water Supply Connection
Inspect the supply line where it connects to the bottom of the tank and the valve.
If water or drips appear around these connections, tighten the nuts slightly with an adjustable wrench. Avoid over-tightening.
If the supply line is leaking or looks worn or damaged, replace it.
2. Inspect the Tank Bolts
Look underneath the tank for moisture around the bolts that mount the tank to the bowl (only on a two-piece toilet).
Tank bolts use rubber washers to create a watertight seal. When these washers wear out, water can leak between the tank and bowl.
Tighten the nuts slightly or replace the bolts and washers if necessary.
3. Check the Flush Valve Gasket
If water appears between the tank and the bowl, the flush valve gasket beneath the flush valve seat may be worn.
Turn off the water supply, remove the tank, and replace the gasket that seals the flush valve to the bowl.
4. Look for Cracks in the Tank
Examine the tank carefully for hairline cracks.
Cracked porcelain tanks cannot be repaired safely. If this is the problem, you’ll probably have to replace the toilet tank or the entire toilet.
5. Test the Toilet
Turn the water supply back on and allow the tank to refill.
Flush several times while checking for leaks around the supply connection, bolts, and tank base.
When the Problem May Be More Serious
If water continues leaking after replacing bolts or seals, the problem may involve:
- A cracked tank
- Improper tank installation
- Severe corrosion of tank hardware
In these cases, replacing the tank or the entire toilet may be the safest solution.
Preventing Toilet Tank Leaks
To reduce the chance of future leaks:
- Replace aging supply lines during repairs
- Avoid over-tightening tank bolts
- Inspect tank hardware periodically
- Replace rubber washers that show wear
These simple maintenance steps can prevent many common toilet leaks.
To Hire a Plumber…
If the repair turns out to be more complicated than expected, you can always find a plumber near you.
For hiring advice, see Trade Secrets for Hiring the Right Plumber.
Related Articles
If you’re not sure what’s causing the problem, see our
Toilet Repair and Troubleshooting Guide for a complete diagnostic overview.
Also see:
