Quick Answer: If you find a pipe leaking under your kitchen or bathroom sink, shut off the water supply using the local shutoff valves underneath the sink (turn clockwise until they stop). Place a bucket or towel under the leak to catch dripping water. Dry the area and identify where the leak is coming from: the supply line connections, the drain P-trap, the faucet connections, or a corroded pipe wall. Small leaks at threaded connections can sometimes be tightened or resealed. Leaks from corroded pipe walls, cracked fittings, or the garbage disposal connection require professional repair. Do not ignore even a small leak, as water damage to cabinet floors, subflooring, and surrounding walls happens faster than most homeowners expect.
You open the cabinet under the kitchen sink to grab a trash bag and your hand lands in a puddle. The bottom of the cabinet is wet, the wood is starting to warp, and there is a steady drip coming from somewhere behind the garbage disposal. Or maybe you noticed a musty smell under the bathroom vanity and found the P-trap connection weeping onto the shelf below.
In Lyons homes, under-sink leaks are one of the most common plumbing calls we receive, and they are also one of the most damaging when they go undetected. A small drip that goes unnoticed for weeks can rot cabinet floors, damage subflooring, promote mold growth, and attract pests. The good news is that most under-sink leaks are repairable, and knowing what to do in the first few minutes makes a big difference in limiting the damage.
Step One: Stop the Water
If the leak is coming from a supply line or faucet connection (the pressurized water side), turn off the local shutoff valves under the sink. Most Lyons homes have oval-shaped shutoff valves on both the hot and cold supply lines beneath each sink. Turn them clockwise until they stop.
If the shutoff valves are stuck, corroded, or do not fully stop the flow (common in older Lyons homes where the valves have not been turned in decades), shut off the main water supply to the house. Our guide to handling plumbing emergencies in the Lyons area covers how to locate your main shutoff.
If the leak is from the drain side (P-trap, drain tailpiece, garbage disposal connection), you do not need to shut off the water supply because drain pipes are not pressurized. Just stop using the sink until the repair is made.
Step Two: Identify Where the Leak Is Coming From
Under-sink plumbing has several connection points, and the source of the leak determines the repair. Dry everything with a towel first, then use a flashlight to watch where water appears as you slowly turn the water back on (for supply-side leaks) or run the faucet briefly (for drain-side leaks).
Supply line connections. The braided stainless steel or chrome supply lines that connect the shutoff valves to the faucet can develop leaks at the compression fittings on either end. Tightening the fitting with an adjustable wrench sometimes stops the leak. If the supply line itself is cracked or bulging, it needs replacement. Supply lines are inexpensive and available at any hardware store.
Faucet base or connections. Leaks at the base of the faucet or where the faucet supply lines connect underneath often indicate worn O-rings or gaskets inside the faucet body. This is a common issue in older Lyons homes with original fixtures that have been in service for 20 or more years.
P-trap connections. The curved drain pipe (P-trap) under the sink connects with slip-joint nuts that can loosen over time, especially in kitchens where the cabinet is frequently bumped while storing or retrieving items. Tightening the slip-joint nut by hand or with slip-joint pliers often resolves the leak. If the P-trap itself is corroded or cracked (common with old chrome or brass traps), the entire trap assembly should be replaced.
Garbage disposal connection. Kitchen sink leaks frequently originate at the flange where the garbage disposal connects to the sink basin, or at the dishwasher inlet on the side of the disposal. The mounting ring can loosen over time, and the gasket between the disposal and the sink can deteriorate.
Corroded pipe walls. In Lyons homes with original brass, chrome, or galvanized drain fittings, the pipe walls themselves can corrode through and develop pinhole leaks. When the pipe wall is the source, the fitting or pipe section needs replacement rather than repair.
Step Three: Decide Whether to DIY or Call a Plumber
Some under-sink repairs are straightforward for a handy homeowner. Others require professional tools and experience.
You can likely handle it yourself if the leak is from a loose slip-joint nut on the P-trap, a supply line that needs tightening, or a clogged aerator causing water to spray at the faucet base. These are mechanical adjustments that require basic tools and no specialized plumbing knowledge.
Call a plumber if the leak is from a corroded pipe wall, the shutoff valves will not fully close, the garbage disposal mounting assembly is failing, or you have attempted a repair and the leak persists. Also call a plumber if you notice water damage that extends beyond the cabinet interior to the surrounding flooring, walls, or the ceiling of the room below. Chicago Sewer Experts handles under-sink repairs throughout Lyons and can typically resolve the issue in a single visit.
Why Small Leaks in Lyons Homes Cause Big Damage
The danger of an under-sink leak is not the leak itself. It is the fact that it is hidden. Water pooling inside a closed cabinet can damage the cabinet floor, saturate the subflooring beneath, and wick into adjacent drywall without any visible signs from outside the cabinet.
In Lyons homes built before the 1970s, the subflooring is often plywood or even original hardwood planking. Once these materials absorb water, they swell, soften, and eventually rot. Mold begins growing on wet organic materials within 24 to 48 hours in enclosed spaces like sink cabinets. The Environmental Protection Agency recommends addressing water intrusion within that window to prevent mold establishment.
Our post on big problems caused by small leaks covers the full scope of damage that seemingly minor leaks can cause when they go undetected.
Make it a habit to check under your sinks monthly. A quick look with a flashlight takes 30 seconds and can catch a problem before it causes hundreds or thousands of dollars in secondary damage.
Frequently Asked Questions
Can I use plumber’s tape to fix a leaking pipe under my sink? Plumber’s tape (PTFE thread seal tape) can stop leaks at threaded connections where two pipes screw together. It does not work on slip-joint connections, compression fittings, or cracked pipe walls. If you are unsure what type of connection is leaking, a plumber can identify it and apply the correct repair.
Why does the pipe under my sink keep leaking after I tightened it? If tightening a connection does not stop the leak, the gasket or washer inside the fitting is likely worn, cracked, or missing. Over-tightening a fitting with a bad gasket can actually make the leak worse or crack the fitting. Remove the connection, inspect the gasket, and replace it if it shows any deterioration.
How much damage can a small drip under the sink cause? A faucet dripping at one drop per second wastes over 3,000 gallons per year. But the water damage is the bigger concern. Even a slow drip inside a closed cabinet can saturate the cabinet floor, subflooring, and surrounding materials within days. Mold growth can begin within 48 hours on wet surfaces. The sooner you address the leak, the less secondary damage you will face.
Should I replace all the plumbing under my sink at once? If one component has failed due to age and corrosion, the other fittings under the same sink are likely in similar condition. Replacing the entire trap assembly, supply lines, and shutoff valves at the same time is often more cost-effective than making individual repairs over the next year as each component fails. A plumber can assess the condition of all components and recommend the most practical approach for your Lyons home.
Pipe leaking under your sink in Lyons? Call (708) 398-7600. Chicago Sewer Experts is right here in Lyons and available 24/7 for plumbing repairs.
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