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Leak under the sink? How to stop it and when to call a plumber

General home information from Prufloop. Updated October 28, 2026.

The short answer. Most leaks under a sink come from a loose slip nut on the drain trap, a worn supply line, a failing shut-off valve or the faucet base. Turn off the shut-off valves under the sink (clockwise), dry everything, run water and watch for where drips start. Hand-tighten loose trap nuts; replace cracked supply lines; call a plumber for valve or pipe leaks.

Safety first. If water is near outlets, a disposal or other wiring, turn off that circuit at the breaker before reaching in.

What you can safely check

Turn off both shut-off valves under the sink. If they won't close, use the home's main water shut-off.
Put a dry towel or paper towel on the cabinet floor and dry the pipes so you can see where new drips form.
Run water with the stopper out. Drips at the curved trap point to the drain side; drips with the faucet off point to the supply side.
Hand-tighten plastic slip nuts on the trap. Don't over-tighten with a wrench; plastic cracks.
Check for soft or stained cabinet floors, which can mean the leak has been going a while.

When to call a plumber

The shut-off valve itself drips or won't close
The leak is from a pipe joint, the wall or the faucet body
There's mold or a soft, damaged cabinet floor
You have a slow leak you can't find

What a plumber will usually do

Finds the exact source with the system under pressure
Replaces valves, supply lines, traps or faucet parts
Checks for hidden damage in the cabinet and wall

Asking an AI assistant to book it

Once Prufloop launches (planned for Q4 2026 around Charlotte), you'll be able to ask the AI assistant you use something like this, and it can book a verified pro at a posted price in a real open slot. This is how it's planned to work; no assistant is connected yet.

Example request. “There's a leak under my kitchen sink and the shut-off valve drips. Book a licensed plumber in Concord who can come tomorrow morning.”

Before a job is booked, you see the pro's posted price, including any trip or diagnostic fee. Anything extra needs your OK first. When the work is done, you confirm it's fixed with a quick text. That's Proof of Done™.

Questions

Can I keep using the sink with a small drip?

Put a container under it and turn off the shut-off valves when you're not using the sink. Even small leaks damage cabinets and can grow mold within days.

Where is my main water shut-off?

In many Charlotte-area homes it's where the water line enters the house, often in a crawl space, garage or utility room, with a second valve at the meter by the street.

Can my AI assistant book a plumber for this through Prufloop?

Not yet. Prufloop is being built so the AI assistant you already use can book a verified plumber at a posted price, starting with the Charlotte-area pilot planned for Q4 2026 in Mecklenburg, Union, Cabarrus, Iredell, Gaston and Lincoln counties in North Carolina, plus York and Lancaster counties in South Carolina. No AI assistant is connected yet.

Are you a Charlotte-area plumber?

Free to join. Only pay on jobs completed: 10% on jobs under $2,500, less on bigger jobs, charged when the job is marked done. No lead fees. Founding pros get a guaranteed spot and founding terms locked for 24 months.

Secure your spot

How it works for pros