A kitchen sink leak usually shows up by surprise: a damp box, a warped shelf liner or a puddle at the back of the cabinet. In a Bossier City kitchen, that cabinet holds supply lines, a faucet, a drain, and often a disposal and a dishwasher hose. Here is how to find which part is dripping, what you can safely do, and when to call for help.
Why Water Ends Up in the Sink Cabinet
Every fitting under the sink belongs to one of two systems, and they fail differently. The supply side carries water to the faucet and dishwasher. It stays under pressure all day, even with every tap closed, so a weak joint there can weep around the clock.
The drain side works by gravity: water leaves through the basket strainer, drops down the tailpiece, passes through the P-trap and runs into the trap arm in the wall. Those parts sit mostly empty, so a drain-side kitchen sink leak shows up only while water flows out.
That timing is the key. Once you know when the drip happens, you are close to knowing where it starts, and the tests below make that timing easy to see.
Supply-Side Leaks: Lines, Nuts and Angle Stops
Most kitchens have two shutoff valves under the sink, called angle stops. A flexible supply line, often braided stainless, runs from each stop to the faucet, and the hot-side stop may also feed the dishwasher.
- Compression nuts: the nut at each stop squeezes a brass ferrule onto the pipe, and a bumped pipe or loose nut lets water bead there.
- Connector ends: the rubber washer inside each connector nut can harden and seep.
- The line itself: rust on the braid, a kink or a bulge means the inner hose is failing.
- The valve stem: an older stop can drip from its handle after someone turns it.
Supply-side water appears whether or not anyone uses the sink, which makes this kitchen sink leak the easiest to spot. BrassCraft and other makers sell separate faucet and dishwasher connectors, so match the fixture and fitting size.
Drain-Side Leaks: Strainer, Tailpiece and P-Trap
The drain starts at the basket strainer, the metal cup in the sink bowl. It is sealed from above with plumber's putty and from below with a rubber gasket and a large locknut. When the putty dries out or the locknut loosens, water held in the sink seeps down around the strainer.
Below it, the tailpiece drops into the P-trap, and each joint uses a slip nut and a tapered washer. Those washers shift when the trap gets bumped, and older ones harden and stop sealing.
A drain-side leak usually wets the trap and the cabinet floor right below it. A slow drain makes it worse, because water sits higher and reaches joints that normally stay dry. In that case, clogged kitchen sink repair may be part of the fix.
Faucet, Sprayer, Dishwasher and Disposal Leaks
Fixtures and appliances leak too, each with its own timing.
- Faucet base: worn O-rings in a swivel spout let water escape at the base while the faucet runs, and it can drip onto the supply lines and pass for a supply leak. Our faucet repair service covers this.
- Sprayer hose: a pull-down or side sprayer hose can crack or leak at its connector, but only while water flows.
- Dishwasher drain hose: a loose clamp at the disposal inlet or branch tailpiece leaks only when the dishwasher pumps out.
- Garbage disposal: leaks can start at the sink flange, the discharge tube or the dishwasher inlet. The InSinkErator leak guide notes that a drip at the bottom may be running down from the mounting assembly, so check there first. A cracked housing generally means a new unit, which our garbage disposal service handles.
How to Trace a Kitchen Sink Leak With Paper Towels
Dry paper towels make a reliable leak detector, because one drop leaves a clear mark. Empty the cabinet, wipe every fitting dry, lay towels across the floor, and test one system at a time.
- Leave everything off: wait an hour. Wet towels point to the supply side.
- Fill the sink: plug the drain and run the faucet. A wet spot points to the faucet base, sprayer hose or strainer seal.
- Pull the stopper: let the full bowl drain. New water points to the tailpiece, slip nuts or P-trap.
- Run the appliances: run the disposal and a dishwasher drain cycle.
Hold a fresh towel to each joint to find the exact drip. In a humid summer, a cold line can sweat, dampening the whole pipe evenly instead of one fitting. If every joint stays dry, check the caulk seam at the countertop. If the cabinet still gets wet, the water may be coming from inside the wall, a job for water leak detection.
A Bossier City Scenario You Might Recognize
Picture a family whose cabinet floor under the kitchen sink has a dark ring near the back, and the particleboard feels puffy. The towels stay dry overnight and while the sink fills, but when a full bowl of dishwater drains, the towel under the P-trap turns wet within seconds.
That pattern rules out the supply lines, since they would have wet the towels overnight. It also makes the faucet and strainer unlikely, because both were tested while the bowl filled. The evidence points to a drain-side slip joint, most likely a shifted or hardened washer at the trap or tailpiece. The swollen floor says this kitchen sink leak has dripped slowly for weeks. Drying the cabinet floor matters as much as fixing the joint.
Safety Notes
- Shut off the angle stops first: turn each handle clockwise before loosening a supply fitting. If a stop will not turn, close the main shutoff instead.
- Keep a bucket handy: a P-trap holds standing water, so set one under it first.
- Go easy on plastic slip nuts: snug them by hand. Overtightening can crack the nut and make the leak worse.
- Do not force old valves: a corroded stop can snap at the pipe and release water at full pressure.
- Keep the disposal off: a bumped wall switch can start the motor, so leave it switched off while you work and keep hands out of the grinding chamber.
- Replace aging supply lines: swap a rusted, kinked or bulging line instead of tightening it.
- Dry the cabinet quickly: the EPA guide to mold and moisture says drying wet materials within 24 to 48 hours helps prevent mold growth.
When to Call a Professional
Call when a supply line or angle stop leaks and you are not comfortable replacing it, or when a stop will not close fully. Call as well when a kitchen sink leak keeps returning after you reseat the washers. The trap may be cracked or misaligned.
Some signs mean a leak has run for a while. The cabinet floor swells or feels soft, a musty smell lingers after drying, or dark spots appear on the cabinet back.
A disposal leaking from its body, a faucet leaking at the base, or water you cannot trace are good reasons to have Mark Johnson & Sons Plumbing take a look. The EPA's Fix a Leak Week page lists dripping faucets and leaking valves among common household leaks.
Frequently Asked Questions
Why is there water under my sink only when the dishwasher runs?
That timing points to the dishwasher drain hose or its connection at the disposal or tailpiece. The hose only carries water while the dishwasher pumps out. A leak at the dishwasher supply connection would drip all the time, because that line stays under pressure.
Can I just tighten the P-trap slip nuts?
For a small drip, often yes: snug the nut by hand and test again. If it still leaks, the washer has likely shifted or hardened and needs reseating or replacing.
Is a slow drip under the sink urgent?
A kitchen sink leak on the supply side is under constant pressure and can worsen without warning, so treat it as a priority. A drain-side drip is less urgent, but wood that stays wet invites mold.
Get Your Kitchen Sink Leak Traced
Before you call, run the paper towel test and write down when the water appears. Is it there with everything off, while the faucet runs, while the sink drains, or while the dishwasher or disposal runs?
Note which fitting is wet and roughly how old the supply lines and faucet are, and take a photo of the cabinet floor. Mention any recent work under the sink, such as a new faucet or disposal. If water is spreading fast, close the angle stops first.
Then reach Mark Johnson & Sons Plumbing through our contact page, or book a time online. With your notes in hand, a technician can go straight to the likely source, confirm it, and explain the repair before work begins.