You open the cabinet to grab the dish soap and the shelf feels soft under your hand. Maybe there is a dark ring on the wood or a sour smell. Most wet-cabinet calls start with a small amount of water that has fed the same spot for days.
A ten-minute triage checklist for a wet sink cabinet
- Empty the cabinet and set the contents on a dry surface. Cleaning products and paper goods soak up water and hide the real wet area.
- Close the two angle stops under the sink (clockwise) and the dishwasher supply valve if you can find it. If a stop will not turn, shut off the main valve for the house.
- Dry the cabinet floor with towels, then lay a dry paper towel under each connection. The first towel to darken points at the source.
- Run the faucet for one minute, then the disposal, then the dishwasher drain cycle, checking the towels between each test. A leak that only shows up on one test names its source.
- Press a screwdriver tip into the cabinet base and the toe-kick board. If it sinks in or the surface crumbles, the board has absorbed water for a while.
- Photograph the cabinet, the connections and the floor beside it before you remove anything.
Four common sources and what each one means
| Source | What you notice | Water type | Typical fix |
|---|---|---|---|
| Braided supply line or angle stop | Steady drip, damp cabinet floor even when no one uses the sink, sometimes a rust or mineral crust at the nut | Clean supply water when fresh | Replace the line or the stop |
| P-trap or slip nuts | Water only after the sink drains, wet under the bowl | Used water with food and grease | Retighten or replace the trap and washers |
| Disposal body or seal | Drips from the bottom or the flange when the disposal runs | Used water with food waste | Replace the unit or reseal the flange |
| Dishwasher hose or drain loop | Wet cabinet floor and a wet edge on the next cabinet after a wash cycle | Dirty water with detergent and grease | Replace the hose or clamp and check the high loop |
What swells first, and why the cabinet floor goes before the walls
Most builder-grade kitchen cabinets use particleboard or medium-density fiberboard for the base and shelf, often covered with a thin laminate. Once water gets under that skin, the board drinks it like a sponge. It swells, loses its grip on screws and then crumbles when you press it. Plywood boxes and solid wood frames survive far better and can often be dried and kept.
Water also moves sideways. It slips under the toe-kick, travels along the subfloor and shows up in the flooring beside the cabinet run or in front of the dishwasher. Laminate and engineered planks swell at their seams, vinyl lifts at its edges, and hardwood cups over the following days. The drywall behind the sink wicks water upward from its bottom edge, sometimes several inches.
How the wet materials get dried
A technician starts with a moisture meter, which reads wetness in wood and drywall that your eyes cannot see, and often a thermal imaging camera to trace the cool, damp patch across the floor. The goal is to find the edge of the wet area, not just the center of the puddle. Readings are logged so there is a starting number and a finish line.
To dry a closed cabinet, the crew removes the toe-kick and sometimes a section of wall base so air can reach the cavity. Small air movers push dry air through, and an LGR dehumidifier pulls moisture out of the room. If the source was drain-side water, surfaces are cleaned before drying starts.
The EPA's target is 24 to 48 hours, though full drying often runs a few days. Our water mitigation crews work to the ANSI/IICRC S500 standard, and a company should be able to explain how it applies that standard to a kitchen job.
Dry it or replace it: a quick decision table
| Material | Usually dried | Usually replaced |
|---|---|---|
| Particleboard or MDF cabinet base | Light, same-day dampness with no swelling | Swollen, soft, crumbling or peeling laminate |
| Plywood or solid wood cabinet box | Most cases, including surface stains | Delaminated plies or a persistent odor |
| Laminate countertop on a particleboard core | Dry top with no seam lifting | Raised seams around the sink cutout |
| Drywall behind the sink | Clean supply water caught early, firm to the touch | Soft, stained, bubbled or wet from drain-side water |
| Vinyl, laminate or engineered flooring | Isolated edge wetness, lifted and dried quickly | Cupped, swollen or lifting seams |
Once the wet base, drywall and flooring are out, water damage repair rebuilds the cabinet bottom, patches and textures the wall, and matches the floor. New materials over a damp cavity just get wet again, so drying comes first.
When a sink leak is a restoration job and when it is a plumber's job
A plumber fixes the leak. A restoration crew dries and rebuilds what it wet, usually in that order. Call a crew when the base is swollen, the smell is sour, the flooring has moved or the wall behind the sink is damp.
If the damage reaches past the cabinet into a wall or the next room, the neighboring areas matter too. Homes in Woodland Hills, just south of West Hills, and Canoga Park, to the east, see the same pattern of small kitchen leaks that travel along subfloors. Not sure how far yours has gone? Call (818) 337-2642 and describe what you see.
Permits, licensing and insurance wording for a sink repair in Los Angeles
LADBS's Express Permits bulletin names two items that touch a sink job: replacing plumbing fixtures (III.2) and replacing drywall in single-family homes and duplexes (I.22). Express means no plan check, but the permit itself still has to be pulled. So a new sink or faucet may come with paperwork, and a quick question to the department or your contractor settles it before work begins.
Under Contractors State License Board rules, a project whose labor and materials add up to $1,000 or more calls for a licensed contractor. That trigger was $500 until January 1, 2025. Plumbing sits under classification C-36. A new cabinet base plus a plumber's visit can cross $1,000 fast, so look up the license on the board's site before you sign.
California's insurance department separates a sudden, accidental release of water, which a policy typically covers, from seepage or ongoing leaks, which it typically excludes. A line that split overnight and a nut that wept for a year can land on opposite sides of that line. Its claims guide adds that old leaks may have mold behind them, so phone the adjuster before you clean up.
Source: LADBS Express Permits bulletin, CSLB licensing pages, California Department of Insurance residential guides
Questions before you decide? Call (818) 337-2642 and describe what you see.
Questions about water under a kitchen sink
Does a kitchen sink repair in West Hills need a city permit?
Possibly. City building rules list a fixture replacement under Express Permits, so a permit is pulled without a plan check. Tightening a slip nut or swapping a hose is routine upkeep. Replacing the sink, faucet or drain is where paperwork may start. Put the question to LADBS or your plumber before the job, and file any permit receipt with your records.
Can I just run a fan and let the cabinet dry on its own?
If the board is only damp and the leak was caught the same day, towels, an open door and a fan may be enough. If the cabinet base feels soft, the laminate is lifting or the smell is sour, water is likely held inside the board and wall cavity. Only a moisture meter can tell you which case you have. Guessing leaves wet material behind, and the EPA's drying target is one to two days.
Will the leak under my sink be covered by insurance?
That depends on your policy and on how the leak happened. In California, a sudden burst usually sits on the covered side of a homeowners policy, while seepage and slow leaks usually sit on the excluded side. Read your policy's water damage wording, photograph everything, keep the failed part and ask your insurer before you put in permanent materials.
How do I know if the cabinet needs to be replaced?
Press a screwdriver tip into the base and the toe-kick. Swollen, crumbling or peeling particleboard rarely returns to shape and is usually replaced. Plywood or solid wood boxes can often be dried and kept. A moisture meter reading after drying, not appearance, decides whether any board stays.
How long does mold take to start under a leaking sink?
Mold needs moisture, and the EPA's guidance is to get wet areas dry in 24 to 48 hours. A cabinet that stays damp for days is at risk. Testing and removal follow ANSI/IICRC S520, and any health question belongs with your physician.