Shut off the under sink isolation valves for hot and cold water, contain the water with a bucket and towels and watch where it first appears. If you cannot stop the flow at the valve, shut off the home’s main supply and call a licensed plumber: many permanent repairs require professional attention beyond safe DIY limits.
TL;DR:
- Most leaks from supply hoses or fittings are urgent because they run at mains pressure and won’t stop on their own, requiring prompt professional repair.
- Temporary fixes such as silicone tape or epoxy are useful for buying time, but only when properly cured and used within safe limits, especially for wastewater pipes.
- Common failure points include worn p-traps, corroded hoses, and faulty washers, with PVC and PEX as typical materials chosen for durability and ease of repair.
- Emergency situations involve continuous water flow, water reaching electrical devices, or contamination, often costing several hundred to over a thousand dollars depending on complexity.
- Homeowners should isolate the leak first, diagnose whether it is on the supply or waste side, then decide if professional help is needed immediately based on water spread and safety risks.
Table of Contents
- Immediate steps to limit damage in the first 10 to 20 minutes
- How to identify where the leak is actually coming from
- Temporary emergency fixes you can use safely (and when not to attempt them)
- Permanent repair options and what to expect from a plumber
- When a leak is an emergency, and what it typically costs
- Publisher perspective: how Priority Plus Plumbing approaches under sink leaks
- What homeowners get wrong about under sink leaks
- Book a repair or emergency callout
- Sources
- FAQ
Immediate steps to limit damage in the first 10 to 20 minutes
The first few minutes matter most. Cabinets, flooring and nearby electrics can suffer lasting damage if water sits for even a short time, so work through these steps in order.
- Clear the cabinet of stored items, cleaning products and bin bags so you can see the leak clearly.
- Place a bucket under the drip and lay towels or an old blanket across the cabinet floor to protect the surrounding area.
- Turn off the hot and cold isolation valves under the sink if they move smoothly; these are usually small oval or lever handles on the pipes behind the cabinet.
- If a valve is seized, cracked or the leak continues after closing it, shut off the home’s main water supply at the meter or stopcock.
- Dry all fittings with a cloth, then watch closely to see exactly where water reappears first.
- Check whether the water has reached power points, appliances or the cabinet base, wall or floor. If it has, treat the situation as an emergency and stop using nearby electrics.
Clearing the cabinet also gives you a proper look at hoses, fittings and the trap, which helps whether you are attempting a temporary fix or describing the problem to a tradesperson over the phone.
Pro Tip: Keep a torch and an adjustable spanner in the cabinet under your sink. A seized isolation valve is far easier to deal with when you can see it properly and apply gentle, even pressure.
How to identify where the leak is actually coming from
Once the water is contained, the next job is working out whether the leak is coming from the supply side or the waste side. This changes both the urgency and the fix.
- Dry every fitting, then run the tap briefly and watch for the first point where water reappears.
- Wet braided supply hoses, a damp isolation valve body or a weeping compression fitting point to a supply-side leak, usually under constant water pressure.
- A wet p-trap, a loose tailpiece connection or slow draining combined with pooling water point to a waste-side leak from the drain.
- Clear water usually means a supply leak; water carrying food particles or a waste odour means a drain leak, which carries more hygiene risk.
- Photograph the leak area before you touch anything. It helps a plumber diagnose the fault quickly over the phone, as noted in Sydney Water’s fault reporting guidance.
Supply leaks tend to be more urgent because they run at mains pressure and will not stop on their own. Waste leaks are usually slower but still need attention, since standing wastewater is a hygiene concern in a kitchen cabinet.
Temporary emergency fixes you can use safely (and when not to attempt them)
A temporary fix buys time until a permanent repair can happen. It is not a substitute for one, and some situations are outside safe DIY limits altogether.
- Isolate the affected valve, keep the bucket and towels in place, and unplug any nearby appliances if it is safe to reach the power point without standing in water.
- Self-amalgamating silicone tape works well on small pinhole leaks in supply pipes or hose fittings; wrap it under tension and allow the full cure time stated on the packaging before restoring pressure.
- Epoxy putty suits small accessible holes or a cracked section of plastic waste pipe; press it firmly around the damaged area and let it cure fully before running water again.
- A rubber patch held with a jubilee clip can temporarily seal a larger split in a waste pipe, though it is only a stopgap measure.
- Do not attempt to cut, solder or replace pressurised supply pipework yourself. This work generally requires a licensed plumber under state licensing rules, and incorrect work risks contamination, scalding or further leaks.
Photograph every temporary fix before covering it up again, and mention it when you call a plumber. It helps them bring the right parts and avoid a wasted first visit.
Pro Tip: Treat any temporary repair on a wastewater pipe with extra caution. Contaminated water carries health risks that a simple supply-line drip does not.
Permanent repair options and what to expect from a plumber
Most under sink leaks trace back to a small number of common failure points, and a licensed plumber will usually address one of these:
- Replacing a worn p-trap, which is often the cheapest and fastest permanent fix for a waste-side leak.
- Re-seating or replacing the sink strainer where the seal around the drain has perished.
- Replacing compression fittings or flexible supply hoses that have corroded or lost their seal over time.
- Swapping worn washers or O-rings inside isolation valves or tap bodies.
- Replacing a longer section of pipe, or relining it, when corrosion is severe, the same fitting has failed repeatedly, or the affected pipework runs under a concrete slab.
Materials matter for longevity. PVC is standard for waste pipework and holds up well under normal household use, while brass fittings resist corrosion better than cheaper alloys on compression joints. Supply lines are typically PEX or copper, and PEX is generally easier to repair without specialist tools, though copper remains common in older homes.
A transparent quote should set out the access assumptions (will the plumber need to remove cabinetry or cut into a wall), what “make-good” work is included once the repair is finished, and whether compliance paperwork and a workmanship guarantee are provided on completion. Most straightforward under sink repairs, such as a p-trap or hose replacement, are completed within an hour or two on-site. Jobs needing wall access, slab penetration or pipe relining take considerably longer and are usually quoted separately once the plumber has inspected the site.
When a leak is an emergency, and what it typically costs
An under sink leak becomes an emergency when any of the following applies: water is flowing continuously and will not stop, you cannot isolate it at the valve or the main, water is spreading into the cabinet, wall or floor, a pipe has burst or corroded through, water is reaching electrical equipment, or the leak involves contaminated wastewater rather than clean supply water. Sydney Water’s guidance on leaks and breaks treats uncontrolled flow and burst pipes as conditions needing immediate attention, including shutting off the affected supply before anyone assesses the damage.
Costs vary with the fault and how hard it is to reach.
| Repair type | Typical cost range |
|---|---|
| Washer or tap hose replacement | A few hundred dollars |
| Burst pipe repair | Several hundred to over $1,000 depending on access |
| Seized isolation valve replacement added to a repair | Typically adds a moderate additional cost due to extra labour |
These figures reflect typical Australian ranges reported by GoingRate’s 2026 plumbing cost calculator. After-hours attendance, concealed or hard-to-reach pipework, and any required make-good work all add to the final bill.
- Ask for the plumber’s licence details before work begins.
- Request an itemised quote that states the isolation point used and what is excluded.
- Confirm whether a workmanship guarantee and compliance paperwork are included once the job is finished.
Publisher perspective: how Priority Plus Plumbing approaches under sink leaks
A local plumbing company runs 24/7 emergency plumbing across Sutherland Shire, Sydney, with over 25 years in the trade. The team handles urgent jobs including burst pipes, blocked drains and hot water failures, using CCTV diagnostics where a fault is not obvious. Jobs come with upfront pricing, clear communication and a workmanship guarantee.
What homeowners get wrong about under sink leaks
The biggest mistake is treating every drip the same way. A slow weep from a compression fitting and a burst supply hose both look alarming at 11pm, but they carry very different levels of urgency, and panicking into an unnecessary after-hours call-out is as costly as ignoring a genuine emergency.
The second mistake is assuming a temporary fix has solved the problem. Self-amalgamating tape and epoxy putty are genuinely useful, but they are a holding measure on a fault that will eventually need proper attention, not a repair.
What actually matters is the sequence: isolate first, diagnose second, decide third. Most homeowners can handle the first two steps safely. The decision about whether to call a licensed plumber immediately or book a routine visit should come down to whether water is contained and whether the fitting involved is something you are licensed and confident to touch, not how dramatic the leak looks at first sight.
— Peter Honey
Book a repair or emergency callout
Once the leak is contained, the next step is getting it fixed properly rather than hoping the temporary patch holds. Priority Plus Plumbing covers the services most relevant to an under sink leak directly.
- Leaking tap repairs and general under sink fittings, booked through the main contact page.
- Burst pipe repairs for supply-line failures that need urgent attention, detailed on the burst pipe repairs page.
- Pipe relining and broader kitchen plumbing work, covered on the plumbing services page.
- Hot water repairs and replacement, where a leak has affected a nearby unit, covered on the hot water repairs page.
When you call, expect a licence check, an itemised quote before work starts, and a workmanship guarantee on the finished job. Get in touch through the Priority Plus Plumbing contact page to arrange a callout.
Sources
- Report a fault | Sydney Water
- Plumbing work in your home | WA Government
- Plumbing cost calculator (Australia 2026) | GoingRate
FAQ
What to do if the sink is leaking underneath?
Clear the cabinet, place a bucket and towels under the leak, then close the hot and cold isolation valves under the sink. If a valve will not turn or the leak continues, shut off the home’s main water supply and arrange a licensed plumber for anything beyond a simple washer or hose swap.
How much does it cost to fix a leak under a sink?
Simple repairs like a washer or hose replacement typically cost a few hundred dollars, while burst-pipe repairs commonly run from several hundred dollars to over $1,000 depending on access, according to GoingRate’s 2026 cost data. A seized isolation valve can add a further $100 to $220 to the job.
What could be causing a water leak under my sink?
Common causes include a worn p-trap, a loose tailpiece, a failed compression fitting, a perished strainer seal or a corroded flexible supply hose. The exact fix depends on whether the leak is coming from the supply side or the waste side.
Is a leak under the sink an emergency?
It is an emergency when water flows continuously and cannot be isolated, when it reaches electrical equipment or spreads into the wall, floor or structure, or when a pipe has burst or the wastewater is contaminated. These conditions call for an immediate shutoff and urgent professional attention, as outlined in Sydney Water’s leak response guidance.