Picture this: you open the cabinet under your kitchen sink to grab the dishwashing liquid and notice the bottom of the cabinet is damp — or worse, there's a small pool of water sitting there. It's one of those moments that sends a chill down your spine because you know something's not right, but you're not sure how bad it is.
The space under your sink is one of the most overlooked areas in any home. Out of sight, out of mind — until it becomes a serious problem. Slow leaks, dripping pipe joints, and failing drain connections can quietly cause mould growth, cabinet rot, and structural water damage over months or years. The good news is that a quick visual inspection every month or two takes less than five minutes and can catch problems early before they escalate.
In this guide, we'll walk you through exactly what to check under your sink, what warning signs to look for, and when it's time to call a licensed Gold Coast plumber.
Signs You Have a Problem Under Your Sink
Not every sink leak is dramatic. Many develop slowly and show subtle signs that are easy to miss if you don't know what you're looking for.
Watch for these warning indicators:
- Water stains or discolouration on the cabinet floor or walls — a yellow or brown ring usually means water has been sitting there repeatedly
- Warped or soft cabinet board — moisture causes MDF and particleboard to swell and lose structural integrity
- Mould or mildew — black, grey, or greenish spots with a musty smell indicate persistent moisture
- Mineral deposits or white residue around pipe joints — this forms when mineral-rich water slowly drips and evaporates
- Rust on metal fittings — corrosion around the p-trap, supply lines, or valves is a sign of ongoing moisture exposure
- Dampness to the touch — run your fingers along every pipe joint and connection; any sign of moisture means something needs attention
If you notice any of these signs, it doesn't necessarily mean you have a catastrophic failure — but it does mean you need to act before it gets worse.
What to Inspect Under Your Sink
The P-Trap
The p-trap is the curved pipe section beneath the drain — named for its P-like shape. Its job is to hold a small amount of water that prevents sewer gases from entering your home. It's also one of the most common spots for leaks.
Check:
- The rubber washers where the p-trap connects to the tailpiece (vertical drain pipe) and the wall drain pipe
- Any visible cracks in the plastic or corrosion on metal p-traps
- The entire joint for moisture, white mineral buildup, or discolouration
P-trap washers harden and shrink over time, causing slow drips that seem minor but can damage cabinets significantly over months.
Water Supply Lines
These are the flexible braided lines that connect your hot and cold water shut-off valves to the tap body. They're under constant water pressure even when the tap is off.
Check:
- The connection points at both ends — where the line meets the valve and where it connects to the tap
- The braided sleeve for any signs of fraying, bulging, or rust stains
- Whether the lines are kinked sharply — kinks create weak points that can split under pressure
Braided stainless supply lines have a typical lifespan of 8–10 years. If yours look worn or feel stiff, replacement is cheap insurance against a burst line.
Shut-Off Valves
There are typically two small valves under each sink — one for hot, one for cold. These should always be accessible and functional. A stuck or corroded valve is a problem you only notice when you desperately need to turn off the water quickly.
Check:
- Turn each valve gently — it should offer smooth resistance and open fully when turned counter-clockwise
- Look for mineral crusting around the valve body or stem
- Inspect the packing nut (small nut on the stem) for any drips when the valve is in use
Drain Connections and Basket Strainer
The basket strainer sits in the drain opening at the sink base. Below it, the strainer body is sealed to the sink with plumber's putty. Over time, this seal fails.
Check:
- Look up at the sink base from inside the cabinet — any moisture around the drain flange suggests the putty seal has deteriorated
- Check the locknut underneath for tightness
- Inspect the connection between the strainer body and the tailpiece
Overflow Area (Bathroom Sinks)
Many bathroom basins have an overflow hole near the rim. Water can sometimes find its way down the overflow channel and create drips inside the cabinet.
Check:
- Run water to the overflow level and watch under the sink for any drips
- Inspect the area where the overflow connects to the drain body for deterioration
How to Perform a Simple Leak Test
If everything looks visually fine but you suspect an intermittent leak, perform a paper towel test:
- Dry the inside of the cabinet and all pipe connections completely
- Place a dry sheet of paper towelling under the p-trap and along pipe connections
- Run both hot and cold water fully for 2–3 minutes
- Check the paper towels immediately and again after 10 minutes
Any wet spots on the paper towels will point you directly to the leak source. This method finds slow drips that are otherwise invisible.
When to Call a Licensed Gold Coast Plumber
While tightening a loose p-trap connection is well within most homeowners' abilities, there are situations where calling a professional is the safer and smarter choice.
Contact a plumber when:
- You find active water pooling or a dripping pipe that won't stop even after tightening
- Shut-off valves won't fully close — this needs replacing before the leak can be properly repaired
- Supply lines show any signs of bulging, corrosion, or fraying (a failing line can flood a room in minutes)
- There's mould present behind the cabinet or on the wall — this often indicates a longer-term leak that needs professional assessment for remediation
- You notice a significant drop in water pressure at the tap, which could signal an internal issue with the supply line or tap body
- Any drain issue that persists after cleaning the p-trap — slow drains under a sink can indicate a partial blockage deeper in the wall pipe
At Coastal Plumbing Professionals, we handle everything from simple p-trap replacements to full under-sink overhauls including new supply lines, shut-off valves, and drain assemblies. We service all Gold Coast suburbs and can usually attend same-day for leak issues. Call us on 1300 590 085.
How to Prevent Under-Sink Problems
Prevention takes minutes and can save hundreds — or thousands — in repair costs.
Monthly habits:
- Open the cabinet and visually scan the area — 30 seconds is all it takes
- Feel along supply lines and p-trap joints for moisture
- Smell for mustiness that suggests hidden mould growth
Every 6 months:
- Perform the paper towel test
- Check shut-off valves for freedom of movement
- Inspect supply lines for age and wear
Every 5–10 years:
- Replace braided supply lines proactively, especially in older homes
- Consider upgrading plastic p-traps to higher-grade PVC or chrome brass
- Have a plumber inspect all under-sink fittings as part of routine home maintenance
Keep the area accessible:
- Avoid cramming cleaning products tightly against pipes — this can cause slow physical damage to supply lines over time
- Use a waterproof liner or tray on the cabinet floor to contain minor drips and make them visible
Final Thoughts
Checking under your sink is one of the easiest home maintenance tasks you can do — and one of the most valuable. A five-minute inspection every month or two gives you early warning of the leaks, corrosion, and seal failures that silently cause expensive damage in Gold Coast homes.
If your inspection turns up anything concerning — stains, moisture, mould, or components that look past their best — don't wait. Plumbing problems under the sink rarely fix themselves, and the longer a small drip continues, the more damage it does.
The team at Coastal Plumbing Professionals are here to help Gold Coast homeowners stay ahead of plumbing problems before they become emergencies. Call 1300 590 085 or visit coastalplumbingprofessionals.com to book an inspection.
Frequently Asked Questions
How often should I check under my sink?
A quick visual check once a month takes less than a minute. A more thorough inspection — including the paper towel test — every 6 months is ideal for most Gold Coast homes.
What does white residue around a pipe joint mean?
White mineral deposits (calcium and magnesium from the water supply) form wherever water is repeatedly dripping and evaporating. It's a clear sign of a slow, ongoing leak that needs to be fixed.
Can I fix a dripping p-trap myself?
Often yes — tightening the slip joint nuts by hand (or with slip-joint pliers) and replacing the rubber washers inside is a DIY-friendly repair. If tightening doesn't stop the drip or the plastic is cracked, call a plumber.
How long do braided supply lines last?
Quality braided stainless steel supply lines typically last 8–10 years. If yours are older than that, or show any signs of rust, fraying, or stiffness, replacing them proactively is strongly recommended.
Is mould under the sink dangerous?
Yes. Mould under the sink indicates persistent moisture and should be taken seriously. The mould itself can cause respiratory issues, and the source of the moisture needs to be fixed before the mould will stop returning.
Resources
- Coastal Plumbing Professionals – Plumbing Repairs
- Queensland Building and Construction Commission – Plumbing Standards
- Gold Coast City Council – Water and Plumbing Guidelines
