Leak under the sink: fix it yourself or call a plumber?

Find the source before reaching for a wrench.

The answer in 2 lines. Stop using the sink and shut off its supply valves if you can reach them safely. If the leak continues or a valve leaks, use the home's main shutoff and arrange help. Dry the cabinet, photograph the damage and identify where fresh water first appears. A simple accessible drain connection may be manageable for an experienced homeowner; a leaking shutoff, damaged supply line, concealed pipe or electrical exposure calls for professional help. Renters should contact their landlord before taking plumbing apart.

Start here

Stop the faucet and any connected dishwasher. Close the sink's hot- and cold-water supply valves gently. If they don't stop the leak, shut off the home's water supply if safely accessible.
Keep away from wet electrical equipment. If the cabinet is safe to approach, remove stored items, place a container under the drip and photograph the wet areas.
Dry visible pipes and connections. Look for the first point that becomes wet again. Don't reopen an uncontrolled supply leak just to diagnose it.

Stop: danger

Wet disposal, outlet or dishwasher connection: don't reach in, unplug wet equipment or operate switches in the wet area. The CDC's electrical-safety guidance says never to use a wet electrical device; apply that precaution before cleanup.
Water covering outlets or cords: stay out. Read the National Weather Service guidance for electrical hazards before approaching a flooded area.

Look for where the drip starts

Where water appears	What it may indicate	What to do
Supply hose, shutoff or connection below the faucet	A pressurized supply leak	Keep the supply off and arrange repair
Curved drain trap or its connections when the sink drains	A loose, damaged or misaligned drain joint	Consider only a clearly understood, accessible repair
Directly beneath the sink's drain opening	A leaking drain assembly or seal	Have the assembly assessed if you cannot identify the repair
Dishwasher hose or disposal area during appliance use	An appliance connection or component leak	Stop the appliance and arrange appropriate service
Wall, floor or cabinet backing	A concealed leak or water traveling from elsewhere	Call a plumber; don't open walls blindly

Water can travel along a pipe before dripping. The lowest wet spot may not be the failed connection. These observations narrow the search; they don't establish a diagnosis.

What not to do

Forcing a corroded valve or tightening a fitting harder without identifying how it seals.
Covering a pressurized leak with tape and treating that as a completed repair.
Removing a drain containing chemical cleaner or mixing cleaning products.
Using a bucket as a permanent solution while the cabinet or wall stays damp.

Where a DIY repair should stop

Limit DIY work to a connection you can identify, isolate and reassemble correctly, where local rules allow homeowner work. Follow the instructions for that assembly rather than assuming all nuts, washers and threads seal the same way. If the parts are cracked, badly corroded or under strain, tightening is unlikely to solve the underlying problem.

Keep the water off while repairing. Afterward, restore service cautiously and check both with the faucet off and while draining water. If fresh moisture appears, stop using the sink and arrange help. Don't leave a newly repaired connection unobserved immediately after restoring water.

For prevention, open EPA WaterSense's home-maintenance guidance and use its leak section to plan inspections and investigate unexplained water use. It supports regular leak checks; it does not replace instructions for your particular fittings.

Who to call, and who pays

Use a plumber licensed as required locally for a leaking shutoff, fixed piping, concealed leak or repair that keeps failing. Ask for a written scope and price. In California, enter the contractor's number in the official license checker and compare the status and business details. Elsewhere, select your state in USAGov's consumer directory and ask which licensing authority applies.

Renters should report the leak in writing and request repair instructions. Responsibility depends on state and local law and the cause. If repairs stall, use USAGov's tenant-rights page to find state housing guidance before withholding rent or deducting repair costs.

For resulting damage, read the NAIC's plumbing-water-damage explanation, then ask your insurer about your own policy. Sudden discharge damage may be covered; that does not establish coverage for the failed part or every slow leak. Save photographs and repair receipts.

Good to know

A closed faucet does not isolate the supply hoses beneath it. Use the supply valves or main shutoff when a pressurized connection leaks.
Tell building management if water may be reaching another unit. Don't assume a dry cabinet surface means the space beneath it is dry.

Illustrative example: Elena finds a wet cabinet in her rental. She stops using the sink, isolates the water and sends photographs to maintenance. The drip appears at a supply connection even though the faucet was off. She leaves the supply isolated and lets the authorized plumber repair it rather than tightening an unfamiliar fitting.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on November 4, 2026, for the United States. Confidence: high for electrical precautions, leak maintenance and the need to check local responsibilities; medium for the troubleshooting patterns and DIY suitability, which depend on the actual installation. This guide is not a diagnosis or a fitting-specific repair manual.