How to find and fix a plumbing leak under your sink
A plumbing leak under your sink rarely announces itself. Here is how Wilmington homeowners find the source fast, fix it, and stop cabinet water damage before it spreads.
The fastest way to find a plumbing leak under your sink is to dry every surface, run the faucet and disposal for two minutes, then watch the supply lines, P-trap, and drain tailpiece with a flashlight - the first bead of water tells you the source. Fixing it usually means tightening a compression nut, replacing a $6 supply line, or resealing the basket strainer, and most under-sink leaks in Wilmington, Delaware stop the same day once you know which joint is weeping. This post walks through detection, the actual repair, 2026 pricing, and the point where a wet cabinet means you should stop and call us.
Wilmington Water Damage Pros handles the drying and repair side of these jobs every week, from the riverfront condos to the rowhouses off Union Street. If you would rather not crawl into a cabinet with a flashlight, we do that too. Homeowners searching for Water Damage Restoration in wilmingtonde, Delaware usually start here, with a drip they ignored for a month.
How to find and fix a plumbing leak under your sink in Wilmington, Delaware
How to find and fix a plumbing leak under your sink in Wilmington, Delaware is a two-part job: locate the exact joint that is leaking, then repair or replace that part before moisture reaches the cabinet floor. The detection half takes about 15 minutes. The repair half ranges from 5 minutes for a loose nut to 45 minutes for a new P-trap assembly.
Under-sink plumbing is a small system with five common failure points:
- Supply lines - the braided hoses running from the shutoff valves to the faucet. These fail at the crimp, not the middle.
- Compression fittings - where the supply line meets the shutoff valve. A quarter-turn with a wrench often ends the drip.
- The P-trap - the curved pipe holding water to block sewer gas. Plastic traps crack; metal traps corrode at the threads.
- The basket strainer - the drain fitting inside the sink bowl. Plumber's putty dries out after 8-12 years and water slips past the rim.
- The disposal connection - the dishwasher hose clamp and the disposal's own mounting ring, both common drippers.
If you have already found standing water in the cabinet, skip straight to drying. We handle plumbing leak water damage cleanup wilmingtonde with truck-mounted extraction and commercial dehumidifiers, because a wet particleboard cabinet floor swells within 24 to 48 hours and never returns to shape.
Signs of a leak under the sink Wilmington homeowners miss
Signs of a leak under the sink Wilmington homeowners miss are almost always indirect - the water shows up somewhere other than the cabinet. A leak that drips once every 90 seconds can run for weeks before you open the doors.
Watch for these:
- A musty smell in the kitchen that does not clear after cleaning. That is mold colonizing wet wood, usually within 48-72 hours of a slow leak.
- Cabinet floor warping or soft spots. Press the cabinet base with your thumb. If it gives, the particleboard is already saturated.
- Peeling paint or bubbling caulk on the toe kick or the wall behind the cabinet.
- Water stains on the ceiling below if the kitchen sits over a basement or a first-floor room.
- A higher water bill with no change in habits. A pencil-thin supply line leak wastes 30 to 60 gallons a day.
- Discolored cabinet interior - dark rings on the wood floor of the cabinet, or white mineral crust around a fitting.
Mineral crust is the giveaway. Calcium and magnesium in Wilmington's water supply deposit a chalky ring wherever a fitting has been weeping for a while. If you see that ring, the leak is not new - it has been there for months.
How do I find a plumbing leak under my sink in Wilmington, Delaware?
To find a plumbing leak under your sink in Wilmington, Delaware, isolate the supply side from the drain side. Supply leaks drip constantly, even when the faucet is off. Drain leaks only appear when water is running.
- Empty the cabinet and dry everything. Paper towels, not a rag - you want to see the first dark spot clearly.
- Wrap each fitting in a dry paper towel. Supply connections, P-trap slip nuts, strainer rim, disposal mount.
- Do nothing for 10 minutes. If a towel darkens with the faucet off, you have a supply-side leak.
- Run hot water for two full minutes. Check the towels again. Now-dark towels point to the drain side.
- Fill the sink and pull the stopper. A leak that only shows on a full-basin drain is a strainer or tailpiece problem.
- Run the disposal for 30 seconds. Water at the disposal's bottom mount means the mounting ring or the dishwasher hose clamp has failed.
If nothing shows after all six steps, the leak may be inside the wall or under the floor - a slab leak or a failed solder joint. That is a different diagnosis, and it is worth having a pro look before you tear into drywall.
How to fix a sink leak Wilmington, Delaware: step by step
Fixing a sink leak Wilmington, Delaware style means matching the repair to the failure point - most under-sink leaks are one of four fixes, and none of them require a permit.
Supply line or compression fitting
Shut off the valve, hold the valve body with one wrench, and tighten the compression nut a quarter-turn with a second wrench. If the drip continues, replace the braided line - they cost $8 to $15 at any Wilmington hardware store and take 10 minutes to swap. Do not overtighten; you will crack the ferrule and make it worse.
P-trap slip nuts
Loosen both slip nuts, slide the trap down, and check the washer inside. A hardened or missing washer is the usual culprit. New washers run under $3. Hand-tighten plus a quarter-turn with channel locks is enough. If the plastic trap itself is cracked, replace the whole assembly - a new 1.5-inch P-trap kit is $12 to $20.
Basket strainer
This one is a 30-minute job. Disconnect the tailpiece, unscrew the strainer's lock nut from underneath, lift the strainer out, scrape the old putty, and reseat it with a fresh bead of plumber's putty. Tighten evenly - a strainer that is cocked will leak again within a month.
Disposal mount or dishwasher clamp
Tighten the disposal's mounting ring with the wrench that came with it. For the dishwasher hose, replace the spring clamp with a stainless worm-gear clamp - the spring type loosens with heat cycles and is the single most common slow leak we find in kitchens.
Once the leak is stopped, dry the cabinet thoroughly. If the wood is soft or the smell lingers, call us for kitchen water damage cleanup wilmingtonde before mold sets in.
How much does it cost to fix a sink leak in Wilmington?
Fixing a sink leak in Wilmington costs $0 to $40 in parts if you do it yourself, or $150 to $350 for a licensed plumber to diagnose and repair it in 2026. The wide range reflects what is actually broken - a compression nut is a $5 fix, a failed strainer reseal is a $200 service call.
Typical 2026 pricing in this area:
- DIY parts - supply line $8-$15, P-trap kit $12-$20, strainer putty $5, worm-gear clamps $2 each.
- Plumber service call - $95 to $175 just to show up, plus parts and labor.
- Full under-sink repair - $150 to $350 for supply, trap, or strainer work.
- Water damage drying - $500 to $1,800 for a wet cabinet, depending on how far moisture traveled into the subfloor or wall cavity.
- Cabinet floor replacement - $250 to $700 if the particleboard has swelled and needs to come out.
The drying number is the one that surprises people. A $12 P-trap washer ignored for three weeks routinely turns into a $900 drying and repair bill, because water wicks into the cabinet base, the toe kick, and sometimes the subfloor beneath.
Common mistakes that turn a small drip into cabinet water damage
The most expensive mistake Wilmington homeowners make is treating an under-sink drip as a cosmetic problem. Water does not stay where it lands.
Watch out for these:
- Putting a bucket under the leak and calling it fixed. The bucket catches the visible drip; humidity still saturates the cabinet walls.
- Caulking over a wet seam. Trapping moisture behind caulk guarantees rot and mold.
- Running a fan and assuming it is dry. A box fan moves air but does not pull water out of particleboard. You need a dehumidifier and, for a real soak, structural drying services wilmingtonde.
- Ignoring the ceiling below. If the kitchen sits over a finished basement, a slow leak stains the ceiling weeks before you notice the cabinet.
- Replacing the cabinet without fixing the leak. We have seen brand-new cabinets ruined in six months because the strainer was never reseated.
Particleboard swells permanently once it absorbs water - it does not shrink back when it dries. That is why catching the leak in the first 24 hours matters so much.
When to call a professional
Call a professional when the leak is not visible at a fitting, when the cabinet floor is soft, or when you smell mold. Those three signals mean the problem has moved past a wrench-and-washer fix.Wilmington Water Damage Pros handles the full job: we find the leak, fix it, dry the cabinet and any wet structure behind it, and test the line before we leave. We work in the older rowhouses and riverfront condos across the city, and we know how these buildings trap moisture in ways newer construction does not. If you have already tried the paper-towel test and cannot pin the source, that is the right time to hand it off.
Frequently Asked Questions
How do I find a plumbing leak under my sink in Wilmington, Delaware?
Dry the cabinet, wrap each fitting in a paper towel, and wait 10 minutes with the faucet off. A dark towel means a supply-side leak. Then run hot water for two minutes - if a towel darkens now, the leak is on the drain side, usually the P-trap or strainer.
How much does it cost to fix a sink leak in Wilmington?
DIY parts run $5 to $40. A licensed plumber in Wilmington charges $150 to $350 for a typical under-sink repair in 2026, including the service call. Water damage drying, if the cabinet got wet, adds $500 to $1,800 depending on how far moisture spread.
Can a sink leak cause water damage in Wilmington, Delaware?
Yes. A drip of one drop every 90 seconds adds up to roughly 30 gallons a month and saturates particleboard within 24 to 48 hours. Mold can colonize wet cabinet wood in 48 to 72 hours, and the subfloor beneath is often affected before you notice.
Who fixes under sink water damage near me in Wilmington?
Wilmington Water Damage Pros handles under-sink water damage across the city - leak repair, cabinet drying, subfloor extraction, and mold prevention. We serve the riverfront, Trolley Square, the Highlands, and the surrounding neighborhoods, usually the same day you call.
Do I need to shut off the water before fixing a sink leak?
Always. Close the two shutoff valves under the sink before loosening any fitting. If those valves are seized or dripping themselves, shut off the main and call a plumber - a broken shutoff valve turns a 10-minute repair into an emergency.
Get help with Water Damage Restoration in Wilmington
If the cabinet is wet, the floor is soft, or you cannot find the source, we will take it from here. Wilmington Water Damage Pros finds the leak, repairs it, and dries the space so mold never gets a foothold.
Call (302) 616-0751 and we will be on our way.