Sink leaking: locate the water path before choosing a repair

Use only checks that match the exact appliance or system and its official guide.

1. Check 1

   Remove stored items, place a dry towel or paper towel under the sink, and observe from outside the cabinet where the first wet mark appears. Do not reach behind a sharp, corroded, or unstable pipe.

   Expected result: The first wet point is at the faucet body, a supply connection, the drain or trap, the cabinet wall, or cannot be located.

   Next step: Photograph the first wet point and continue only with the matching non-invasive observation. Arrange a plumber if the source is hidden or the cabinet material is swelling.

   Stop if: Stop for active spraying, a corroded or unstable pipe, sewage-like water, water near electrical equipment, or a cabinet or floor that is soft or collapsing.

   Why this matters

   Why: The first wet point is more useful than the largest puddle. An uncertain or hidden source means water may be traveling behind the cabinet or wall and should not be diagnosed by replacing a visible part.

2. Check 2

   With the area dry, run the faucet briefly and observe the outlet, handle or handles, faucet base, and underside of the sink without touching wet connections or opening the faucet.

   Expected result: Water drips from the outlet when closed, appears around a handle or base while running, or the faucet remains dry while the cabinet wets.

   Next step: Record which handle and faucet area becomes wet, then close the faucet and arrange the appropriate repair. Do not remove a cartridge or tighten the faucet from symptoms alone.

   Stop if: Stop if the faucet is loose at the sink, water sprays toward an electrical device, the handle is stuck, or the leak cannot be controlled.

   Why this matters

   Why: A faucet outlet leak can involve a worn washer, gasket, cartridge, or aerator; water around the base or handle is a different seal path. A dry faucet shifts attention to supply, drain, trap, overflow, or concealed piping.

3. Check 3

   Look at the visible hot and cold supply hoses, shutoff valves, and faucet connections while the faucet is off and briefly while it runs. Do not loosen a nut, force a valve, or disconnect a hose.

   Expected result: A hose or valve is wet at its connection, the leak appears only while water flows, the valve is corroded or immovable, or the supply path stays dry.

   Next step: If a clearly accessible shutoff closes without force, isolate the affected side and arrange plumbing service. If it will not turn or the leak continues, use the main shutoff only if safe and call a plumber.

   Stop if: Stop for spraying water, a seized or corroded valve, a split hose, water near electrical equipment, or any need to pull the sink or cabinet apart.

   Why this matters

   Why: Water at a supply hose, valve, or fitting indicates a pressurized supply-side leak and is not fixed by changing the faucet washer. A dry supply path keeps the drain or faucet body in scope.

4. Check 4

   Put a dry towel beneath the strainer, drain body, trap, and visible wall connection, then run a small amount of water into the basin and empty it while observing from the cabinet opening. Do not loosen the trap or drain fittings.

   Expected result: Water appears during filling, only while draining, at the strainer or drain body, at a trap joint, or at the wall connection.

   Next step: Record the exact joint and stop using the sink if water is reaching the cabinet or floor. Arrange a plumber for drain disassembly, a wall connection, corrosion, or a leak that persists after the basin is empty.

   Stop if: Stop for sewage-like water, a loose or collapsing trap, a hidden wall leak, severe corrosion, or water spreading into flooring.

   Why this matters

   Why: A leak that starts during draining points toward the drain, strainer, trap, or wall connection rather than the pressurized faucet supply. Water at a wall connection or a corroded trap may require more than a simple seal.

5. Check 5

   Inspect the visible basin, overflow opening, rim, caulk line, and underside of the sink for cracks, gaps, staining, or water appearing only when the basin is filled. Do not pry out caulk or seal over an active leak.

   Expected result: The basin or overflow leaks when filled, the rim or caulk line wets, the underside stays dry, or water appears only below the bowl.

   Next step: Stop filling the basin and document the level and leak location. Arrange repair for a cracked basin, failed overflow or rim seal, or any leak that has damaged the cabinet or wall.

   Stop if: Stop for a cracked or unstable basin, a loose sink, water behind the wall, mold-like growth, or swelling structural material.

   Why this matters

   Why: A basin, overflow, rim, or seal leak can bypass the faucet and drain joints. A dry top with water below may indicate the underside, drain seal, supply, or concealed path and cannot be assigned from the puddle alone.

6. Check 6

   After the sink is dry and no fixture is being used, observe whether new water appears and, if safely accessible, compare the home's water meter before and after a period with all water use stopped. Do not remove a meter lid in an unsafe location.

   Expected result: No new moisture appears, water returns without use, the meter changes, or the meter cannot be checked.

   Next step: Record the timing and arrange a leak investigation when water returns without use or the source remains uncertain. Do not seal cabinets or walls before the moisture source is understood.

   Stop if: Stop for flooding, inaccessible or unsafe meter access, water near electrical systems, or any need to cut into a wall or floor.

   Why this matters

   Why: Water returning with no sink use supports a pressurized or concealed leak elsewhere. A stable dry area does not prove the sink is fixed if the leak occurs only under flow or draining.