Open the cabinet under your kitchen sink right now. If the base board feels soft at the edges, looks darker than the rest of the unit, or the whole cabinet smells faintly musty even after you've wiped it down — that's not a cleaning problem. That's water that's been getting in for a while, and it's doing damage you can't see from the kitchen floor. By the time it shows up as a puddle, the board underneath has usually been swelling for weeks already.

Why this leak hides for so long

A sink cabinet is a closed box. Unlike a bathroom or terrace leak that eventually shows up as a stain on a visible wall, a slow drip under the sink drops straight onto the cabinet base and gets absorbed — no puddle, no obvious sign, nothing until the smell gets bad enough to notice or the door won't close right anymore because the board has warped. In a lot of Bangalore homes we've inspected, the leak had clearly been running for a month or more before anyone opened the cabinet to check.

The three places it actually starts

  • The P-trap joint under the sink — the curved pipe below the drain. The rubber gasket at the joint perishes or the nut loosens with regular use, and it drips at the joint every time water runs.
  • The tap's flexible connector hose — the small rubber washer inside the connector fitting hardens and cracks over a few years, leaking a slow trickle right where the hose meets the tap or the wall.
  • The RO unit's waste or overflow pipe — if your RO unit sits inside the same cabinet, its waste line is often just pushed into a drain opening, not sealed. It slips or leaks slowly and nobody checks it for months.

All three look identical from the outside: a damp patch, a wet spot on the cabinet floor, or just that musty smell. You have to actually get in with a torch to tell them apart.

Damp MDF board doesn't just swell — it grows mold, and mold spreads to the cabinet next to it. Under-sink units are usually joined to the rest of the kitchen carcass, so a leak left alone for a couple of months can turn into a two- or three-cabinet replacement instead of a one-hour pipe fix.

The 10-minute check you can do today

  1. Clear everything out of the cabinet — bottles, bins, cleaning supplies — so you can actually see the base and back panel.
  2. Run your hand along the base board for any softness, swelling or dark discoloration, especially in the corners.
  3. Dry the P-trap joint and connector hoses with a tissue, then run the tap for two minutes and check both again for fresh wetness.
  4. Check the RO unit's waste pipe connection if you have one — it's the most commonly overlooked source.
  5. Smell the back corner of the cabinet with the door shut for a minute first — a musty smell with no visible wetness usually means an older, drier leak that's still worth fixing.

What actually needs fixing versus what can wait

A dripping joint or a perished washer is a same-day fix — tighten, re-seal or replace the connector, and it's done. What can't wait is a base board that's already gone soft or delaminated: at that point the moisture has nowhere to dry out on its own, and mold keeps working even after the leak is stopped. That board needs to come out, dry the cavity underneath properly, and go back in — otherwise you've fixed the pipe and left the actual damage sitting there.

We check the pipe joints, connector hoses and cabinet base for leak damage as part of any kitchen or bathroom inspection — and we'll tell you straight if it's a plumber's job or if the board needs replacing. Call +91-8123083393 for a free on-site check, this week, not next month.

Frequently asked questions

Why does an under-sink leak go unnoticed for so long?+

The cabinet floor is closed off, so a slow drip from a P-trap joint or a tap connector doesn't pool visibly — it soaks into the MDF or plywood base a little at a time. By the time you smell must or see the board swelling, the leak has usually been running for weeks.

What are the three most common causes of under-sink leaks?+

A loosened or corroded P-trap joint under the sink, a perished rubber washer at the tap's flexible connector hose, and a poorly sealed RO unit waste or overflow pipe are the three most common sources in Bangalore kitchens and bathrooms.

Can a swollen cabinet base be repaired, or does it need replacing?+

A cabinet base caught early — swollen but not soft or crumbling — can sometimes be dried out, sealed and saved. Once the board has gone soft, delaminated or grown visible mold, it needs replacing; the leak source still has to be fixed first or the new board fails the same way.

Is a musty smell under the sink always a leak?+

Almost always. A closed cabinet with a musty or damp smell and no leak history is usually trapped moisture from a past drip or condensation off a cold pipe — worth checking now, since it's cheaper to fix before the board swells or mold spreads to the adjoining unit.