To tell where a leak is coming from under the sink, dry the cabinet, pipes and fittings completely. Place paper towel beneath each connection, test one source at a time and trace the water to the highest point that becomes wet first. Water can travel along a pipe or hose before dripping.
Test the Connections in Order
Check with the sink unused: Inspect the isolation valves, flexible supply hoses and tap connections. Moisture appearing while the tap is off indicates a likely pressurised supply-side leak.
Test the tap connections: Run the tap briefly into a bowl so no water enters the drain. Recheck the hoses and connections beneath the tap.
Test the sink outlet seal: Dry the area, insert the plug and add a small amount of water without reaching the overflow. Moisture directly beneath the outlet indicates a possible drain-seal leak.
Test the waste pipe and trap: Release the plug and watch each waste joint and the trap as the water drains. A leak appearing only during discharge is likely on the drain side.
Check for splash entry: If the plumbing stays dry, apply a small amount of water around the tap base and sink rim. Water below may be entering through an unsealed mounting or rim rather than leaking from a pipe.
Use a torch and paper towel to observe individual joints, but do not dismantle, tighten or disturb fittings.
Interpret What You Find
| When water appears | Likely source |
|---|---|
| While the sink is unused | Isolation valve, flexible hose or supply connection |
| While the tap runs into a bowl | Tap connection or flexible hose |
| While water sits in the plugged basin | Sink outlet fitting or seal |
| While water drains | Waste joint or trap |
| After wetting the tap base or rim | Mounting point or sink-rim seal |
These signs narrow down the source but do not prove which component has failed.
Isolate the Leak Safely
For a supply-side leak, close the relevant isolation valve only if it is accessible and turns normally; never force it. If water is escaping quickly or the valve does not stop it, shut off the property’s main water supply if you can reach it safely.
For a drain-side leak, stop using the sink, place a container beneath the drip and dry the cabinet.
Do not touch wet power points, plugs, appliance leads or waste-disposal equipment. Keep away from the area and arrange urgent help if water is near electrical equipment.
What affects the repair price?
We are completely upfront about our pricing and do not believe in hiding behind generic online price ranges or rough phone estimates, because an under-sink leak can stem from anything from a perished trap washer or loose slip-joint to a fractured braided flexible hose or pinhole in concealed copper supply lines. Inspecting the actual plumbing on site enables our plumber to identify the exact failing component, verify water pressure, and check for hidden water damage in surrounding cabinetry. We walk you through a clear task breakdown of the steps required to resolve the problem properly, giving you a firm, fixed upfront price before any work begins—backed by our $0 call-out on approved work.
Stop testing and let our experienced Sydney plumbing team assist you if the leak source is tricky to trace, water is under pressure, or a connection needs repair. Regulated plumbing work in NSW must be carried out by an appropriately licensed tradesperson. Fixed Today has been resolving under-sink leaks and tapware problems for Sydney households since 2011. When you get in touch, our team asks a couple of screening questions about the symptoms you are seeing (such as continuous dripping versus leaking only when draining) and your cabinet setup so our technician arrives in a fully stocked vehicle with the right replacement valves, traps, and hoses for an immediate fix.