Why Is My Toilet Leaking? Causes, Warning Signs and What to Do
A leaking toilet is something most homeowners will deal with at some point. Sometimes it’s obvious, like water pooling around the base. Other times it’s silent, hidden inside the cistern or slowly seeping into the floor underneath.
The important thing is not to ignore it. Even a small toilet leak can waste thousands of litres of water or cause significant structural damage over time. If you’ve noticed water where it shouldn’t be, here’s what could be going on and what steps to take next.

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Common Signs Your Toilet Is Leaking
- Water pooling around the base of the toilet
- A constantly running cistern
- Hissing sounds when the toilet isn’t in use
- Water stains on the ceiling below
- Damp or soft flooring around the toilet
- A sudden increase in your water bill
Why Is My Toilet Leaking at the Base?
- Damage flooring
- Cause unpleasant odours
- Lead to mould growth
- Compromise structural timber
Another possible cause is loose mounting bolts. If the toilet shifts slightly, it can break the seal and create leaks underneath.
Water pooling at the base isn’t something to ignore. Even if it seems minor, it can cause serious long-term damage.
Why Is My Toilet Cistern Leaking?
Leaks from the cistern (the tank at the back of the toilet) are also common.
Worn Inlet Valve
If the toilet constantly runs or refills, the inlet valve may not be shutting off properly.
Faulty Flush Valve or Seal
If water trickles into the bowl long after flushing, the flush valve seal is likely worn.
Loose Tank Bolts
Water dripping from between the tank and the bowl often points to deteriorated rubber washers around the mounting bolts.
Cracked Cistern
Though less common, hairline cracks in older ceramic tanks can cause slow leaks.
These issues may appear small, but a constantly running toilet can waste significant amounts of water each day.
Can a Leaking Toilet Increase My Water Bill?
Absolutely.
A silent internal leak can waste hundreds of litres per day without you noticing. Over weeks or months, this adds up to a noticeable increase in your water bill.
If your bill has increased and your usage habits haven’t changed, your toilet is one of the first fixtures to check.
A simple test is to add food colouring to the cistern and wait 10 to 15 minutes without flushing. If coloured water appears in the bowl, there’s an internal leak.
Is a Leaking Toilet Dangerous?
While it may not seem urgent at first, a leaking toilet can create serious issues.
Prolonged leaks can:
- Weaken subfloor structures
- Damage tiles and grout
- Create mould growth
- Lead to unpleasant odours
- Cause ceiling damage below upstairs bathrooms
In severe cases, long-term leaks can compromise the integrity of the bathroom floor.
Acting early reduces both repair costs and health risks.

Can I Fix a Leaking Toilet Myself?
Some minor issues, like replacing a flush valve seal or adjusting the inlet valve, may be manageable for experienced DIYers. However, there are risks:
- Incorrect installation can worsen the leak.
- Removing a toilet without proper sealing can create drainage issues.
- Hidden leaks may go undetected.
If the leak is coming from the base of the toilet or you’re unsure of the cause, it’s safer to involve a licensed plumber.
Toilets connect directly to your home’s sewer system, so proper sealing and alignment are critical.
How a Plumber Diagnoses and Fixes Toilet Leaks
A licensed plumber will:
- Identify whether the leak is internal or external.
- Check seals, valves, bolts, and connections.
- Inspect the pan seal and floor integrity.
- Replace worn components with quality parts.
- Test the toilet thoroughly after repairs.
If the toilet is older or severely worn, replacement may be recommended instead of repeated repairs.
Professional repairs ensure the leak is fully resolved, not temporarily patched.

Preventing Future Toilet Leaks
While wear and tear is unavoidable, you can reduce the risk of leaks by:
- Avoiding harsh chemical cleaners
- Fixing running toilets early
- Ensuring the toilet is securely mounted
- Checking for movement around the base
Regular inspections help catch small issues before they escalate.


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Hilton Plumbing
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Hilton Plumbing
Final Thoughts
A leaking toilet is never something to ignore. Whether it’s water at the base, a constantly running cistern, or hidden internal leakage, acting early prevents costly structural damage and wasted water.
If you’re unsure where the leak is coming from or the issue keeps returning, professional diagnosis ensures the problem is fixed properly the first time.
Addressing toilet leaks quickly protects your home, your plumbing system, and your water bill from unnecessary damage.














