How to Find a Hidden Water Leak in the Bathroom
A hidden water leak in your bathroom might not seem like a big deal at first, but over time, it can lead to major damage.
From mould growth and peeling paint to high water bills, the signs of a leak can be subtle yet costly if ignored. The tricky part? These leaks often happen behind walls, under floors or inside plumbing fixtures, making them hard to spot.
The good news is that with a little detective work, you can track down the source of the problem before it gets worse. Whether it’s checking your toilet, inspecting under the sink, or testing your water meter, there are several ways to uncover a hidden leak.
In this guide, we’ll walk you through simple steps to help you identify and fix leaks before they cause major damage.
Signs of a Hidden Water Leak
Hidden water leaks in the bathroom can cause serious damage over time, but they often leave small clues. Here are some common signs to watch for:
- Unexplained increase in water bills – If your water usage hasn’t changed but your bill is rising, a hidden leak might be to blame.
- Musty odours and mould growth – Excess moisture from a leak creates the perfect environment for mould and mildew, especially in corners and behind walls.
- Peeling paint or wallpaper – Water seeping through walls can make paint bubble or wallpaper peel.
- Warped or stained flooring – If your bathroom floor feels soft, spongy, or has dark stains, water may be leaking underneath.
- Water stains on walls or ceilings – Brownish stains or damp spots on walls or ceilings below the bathroom suggest a leak from above.
If you notice these warning signs, it’s time to investigate before the damage worsens.
Checking the Toilet for Leaks
Your toilet is one of the most common places for hidden leaks in the bathroom. Even a slow, silent leak can waste a lot of water over time. Luckily, checking for leaks is simple.
Start by adding a few drops of food colouring into the toilet tank (cistern) − don’t flush. Wait about 10-15 minutes and check the toilet bowl. If you see coloured water in the bowl, there’s a leak, usually caused by a faulty flapper valve that isn’t sealing properly.
Also, listen for the sound of running water when the toilet isn’t in use. If you hear a faint hissing noise, there might be a slow leak.
Lastly, check around the toilet’s base for any moisture or pooling water, which could indicate a leak in the seal. If you find any of these signs, replacing worn-out parts or sealing leaks can prevent water waste and costly repairs.

Inspecting the Sink and Taps
Bathroom sinks and taps are common sources of hidden leaks. Even small drips or unnoticed moisture can lead to water waste and damage. Here’s how to check for leaks:
- Look under the sink – Open the cabinet and check for damp spots, water stains, or mould. If the area feels damp or smells musty, there may be a leak.
- Check the pipes and connections – Run your hand along the pipes under the sink to feel for moisture. Tighten any loose fittings and inspect for corrosion.
- Watch for dripping taps – Even a slow, steady drip can waste water and increase your bill. Replacing a worn-out washer or cartridge can fix the problem.
- Listen for unusual sounds – If you hear a faint hissing or dripping when the water is off, there could be a small leak.
Addressing sink and tap leaks early can prevent bigger plumbing issues down the road.
Examining the Shower and Bathtub
Your shower and bathtub see a lot of daily use, making them prime spots for hidden leaks. A small crack in the grout or a slow drip can lead to water damage over time.
Here’s how to check for leaks:
- Inspect the grout and caulking – Cracked or missing grout around tiles allows water to seep behind walls. Reapply caulking or grout where needed.
- Check for damp spots – Look for discolouration, peeling paint, or soft walls near the tub and shower. These signs indicate water may be leaking behind the surface.
- Test the showerhead and tub spout – Turn off the water and watch for slow drips. If you notice leaks, replacing the washer or tightening connections can help.
- Look for standing water – Water pooling outside the tub or shower may mean a problem with the drain or a faulty seal.
Catching leaks early can help prevent costly repairs and mould growth.
Detecting Leaks in the Walls and Floor
Hidden leaks behind walls and under floors can go unnoticed for a long time, but they often leave clues. Start by checking for discolouration, bubbling or peeling paint on the walls.
Water damage can also make drywall feel soft or spongy. If you notice any of these signs, there could be a slow leak behind the surface.
For floors, look for warping, loose tiles or unexplained damp spots, especially near the bathtub, shower or sink. A musty smell in the bathroom can also indicate hidden moisture buildup.
If you suspect a leak but can’t see any visible damage, try using a moisture meter to detect damp areas or an infrared thermometer to find temperature differences caused by water.
Acting quickly can prevent costly repairs and mould growth. If the signs persist, it’s best to call a professional plumber to pinpoint and fix the leak.
Testing the Water Meter for Hidden Leaks
If you suspect a hidden water leak in your bathroom but can’t find any obvious signs, your water meter can help confirm it. This simple test can reveal if water is leaking somewhere in your home − even behind walls or under floors.
First, turn off all the water in your house. Make sure no taps, appliances, or toilets are running. Next, locate your water meter, usually found outside near the front of your property.
Check the meter reading and wait about an hour without using any water. Then, check the meter again. If the numbers have changed, it means water is flowing somewhere − indicating a leak.
For a faster check, some water meters have a small leak indicator (a spinning dial or triangle) that moves even with the slightest water flow. If you detect a leak, it’s time to inspect your bathroom or call a plumber for further investigation.

When to Call a Professional Plumber
Sometimes, finding a hidden water leak in your bathroom requires more than a DIY inspection. If you notice any of the following signs, it’s best to call a professional plumber:
- You can’t locate the source of the leak – If water damage is visible but you can’t pinpoint where it’s coming from, a plumber has specialised tools to detect hidden leaks.
- Your water bill keeps rising – A sudden increase in your water bill, even after checking for leaks, may indicate an underground or internal pipe leak.
- Mould and musty smells won’t go away – Persistent mould growth or a damp odour can mean a long-term leak behind walls or under floors.
- There’s low water pressure – If your sink or shower water pressure drops, a hidden pipe leak could be affecting the flow.
- Structural damage is visible – Warped floors, ceiling stains, or peeling paint are signs of a serious leak that needs expert repair.
A plumber can quickly find and fix the issue before it leads to costly damage.
Take Action Quickly
Hidden water leaks in your bathroom can cause serious damage if left unchecked, but knowing the signs can help you catch them early.
From checking your toilet and sink to inspecting walls and floors for moisture, there are several ways to detect leaks before they get worse. If you notice peeling paint, mould or unexplained water stains, it’s time to investigate.
For leaks that are hard to find, using your water meter or calling a professional plumber can save you time and money. Taking action quickly will help prevent costly repairs and keep your bathroom safe, dry and leak-free.
Please note: This information is provided for advice purposes only. Regulations differ from state to state, so please consult your local authorities or an industry professional before proceeding with any work. See Cyber Plumbers’ Terms & Conditions here.