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A leaking toilet doesn't always look dramatic. Sometimes it's a faint hiss you only notice at night, a damp patch at the base you catch out of the corner of your eye, or a water bill that's crept up for no obvious reason. Whatever form it takes, a leaking toilet is worth taking seriously, since even a small, constant leak can waste hundreds of litres of water a week.
The tricky part is that "leaking toilet" covers several very different problems, each with its own fix. In this guide, we'll walk through the most common causes of a leaking toilet, how to tell which one you're dealing with, and when it's time to call a plumber.
Leaking From Inside the Bowl (Running or Phantom Flushing)
If your toilet keeps making a running or refilling sound even when nobody has used it, water is leaking from the cistern into the bowl.
Common cause: worn flapper valve
The rubber flapper valve at the bottom of the cistern seals the water in until you flush. Over time, it warps, cracks, or develops mineral build-up, and stops sealing properly, letting water trickle continuously into the bowl.
How to check
Add a few drops of food colouring to the cistern without flushing. If colour appears in the bowl within 15 minutes, the flapper valve isn't sealing and needs replacing.
The fix
Flapper valves are inexpensive and straightforward to replace. Turn off the water supply, drain the cistern, unhook the old flapper, and fit a new one matched to your toilet's make and model.
Leaking From the Base of the Toilet
Water pooling on the floor around the base of the toilet, especially after flushing, points to a different problem entirely.
Common cause: worn wax or rubber seal
The seal between the toilet base and the drain pipe beneath it can dry out, crack, or shift over years of use, letting water escape onto the floor with every flush rather than down the pipe.
Common cause: loose toilet base
If the toilet rocks slightly when you sit down, the bolts securing it to the floor may have loosened, which can also break the seal underneath and cause leaking.
Why this one matters
Water leaking at the base isn't just wasteful. Left unaddressed, it can soften and damage the subfloor, especially in older Gold Coast bathrooms with timber flooring, leading to a far more expensive repair than the toilet itself.
Leaking From the Cistern Connections
If water is pooling behind the toilet rather than at the front, the issue is usually with one of the connections feeding or supporting the cistern.
Common causes
- A loose or worn supply line connecting the water inlet to the cistern
- A worn fill valve washer inside the cistern
- Cracks in the cistern itself, often from age or a previous impact
- Loose bolts connecting the cistern to the bowl on two-piece toilets
The fix
Tightening loose connections often resolves minor drips. Cracked cisterns, however, usually need full replacement rather than repair, since sealants don't hold reliably under constant water pressure.
How to Check Which Type of Leak You Have
- Dry the floor and all surfaces around the toilet completely.
- Wait 30 minutes without using the toilet, then check for new moisture at the base, behind the cistern, and around the supply line.
- Listen for a hissing or trickling sound with the bathroom door closed and no other water running in the house.
- Do the food colouring test in the cistern to check for a bowl leak.
- Gently rock the toilet from side to side to check for looseness at the base.
When to Call a Plumber
Some toilet leaks are simple DIY fixes. Others need a licensed plumber, particularly when:
- The leak is coming from the base and the wax or rubber seal needs replacing
- The toilet rocks or feels loose when sat on
- The cistern itself is cracked
- You've replaced the flapper valve, but the running sound continues
- There's visible water damage to the floor or subfloor around the toilet
Replacing a base seal requires removing the toilet entirely, which risks damaging the flange or floor if done incorrectly, so it's often worth having a professional handle it the first time.
If your toilet is leaking and you're in the Gold Coast area, our licensed plumbers provide reliable toilet repairs and installation to get it fixed properly, not just patched.
Preventing Toilet Leaks
- Check your cistern for silent leaks every few months using the food colouring test
- Avoid using in-cistern cleaning tablets long-term, as they can degrade rubber seals faster
- Have loose toilets checked and re-secured before the leak worsens
- Replace flapper valves and fill valve washers every few years as routine maintenance
Final Thoughts
A leaking toilet is rarely just one problem. It could be a simple flapper valve, a failing base seal, or a loose connection behind the cistern, and each needs a different fix. Working out where the water is actually coming from is the key first step, and once you know that, most leaks are straightforward to resolve, whether by yourself or with a plumber's help.
Call Coastal Plumbing Professionals on 1300 590 085 if your toilet is leaking and you're not sure where the water's coming from.
Frequently Asked Questions
How much water does a leaking toilet actually waste?
A running toilet can waste hundreds of litres a day depending on the severity of the leak, which can add up to a significant, noticeable jump in your water bill.
Why does my toilet keep making a running sound after I flush?
This usually points to a worn flapper valve not sealing properly, letting water continuously trickle from the cistern into the bowl.
Is it normal for a small amount of water to appear at the base of the toilet?
No. Any water at the base indicates the seal between the toilet and the drain has failed and needs attention before it damages the floor underneath.
Can I replace a toilet's wax seal myself?
It's possible, but it requires safely removing the toilet, which risks cracking the porcelain or damaging the flange if not done carefully. Many homeowners prefer a plumber for this job.
When is a toilet leak considered an emergency?
If water is actively pooling on the floor, especially near powerpoints or timber flooring, treat it as urgent and shut off the water supply until a plumber can assess it.
Resources
- AS/NZS 3500 Plumbing and Drainage Standards
- Save water at home | Queensland Government
- WaterMark Certification Scheme | Australian Building Codes Board
