Water under the kitchen sink? Stop it, find the source, then read the costs
Updated July 2026 · cleanup costs from published guides; category per IICRC S500; coverage per III guidance
Water in a sink cabinet is deceptive: it's a closed box, so a slow drip soaks the particle-board floor and the wall behind it long before you see it. The first move is to stop the water, not mop it — close the shut-off valves under the sink, then let the cabinet tell you where the leak is. Stop it, find why, then decide what it costs and which bill your insurance actually pays.
First 5 minutes: shut the water off, then dry to find the source
Reach to the back of the cabinet and close the two shut-off valves (the small angle-stop valves feeding the faucet) by turning them clockwise. If a valve is seized or your sink has none, close the main water shut-off for the house. That isolates the leak without a plumber. Then empty the cabinet, dry the base completely, and lay down dry paper towel so you can watch exactly where water reappears — this is the fastest way to tell a pressurized supply leak (wets even with the sink off) from a drain leak (only wets when water runs). Get air moving over the wet cabinet floor and the wall cavity behind it the same day; the instinct-saving sequence is in our first-60-minutes checklist.
Where's it coming from? Five usual suspects — the source sets the cleanup
Once the water's off, find the source — it tells you what to fix and how dirty the water is.
- Supply line or angle-stop valve: under pressure, so it drips or sprays continuously, even with the sink off — usually a corroded braided hose or a failing shut-off. This water is Category 1 (clean) and the cheapest to dry.
- Drain leak (P-trap, slip nuts, tailpiece): only wets the cabinet when water runs down the drain. Carries food waste, so it's Category 2 “grey water” — treat it as contaminated.
- Garbage disposal: leaks from the top drain-flange gasket or the split body of an aging unit — also grey water.
- Faucet base: water seeps down through the deck and runs to the back of the cabinet; often mistaken for a supply leak until you dry and watch.
- Dishwasher hose: the dishwasher's supply or drain connection under the sink can leak there too — check it if the other four look dry.
The water damage — priced by area and category, not the part
Sink-cabinet damage is priced by how much got wet and how contaminated the water is under the IICRC S500 standard, not by the broken fitting. Professional mitigation for clean water (Category 1) — a supply drip caught quickly — prices at roughly $3.75–$5.25 per square foot of affected area; grey water (drain or disposal) costs meaningfully more because contaminated porous materials — the particle-board cabinet floor, soaked drywall, swollen flooring — have to be removed and disposed of rather than dried, and when they come out and get rebuilt, reconstruction adds about $20–$37 per square foot. The clock that matters most is the mold clock: mold can begin growing on damp materials within 24–48 hours, and a sink cabinet traps moisture where it dries slowly — so extraction, airflow and a dehumidifier the same day is what keeps a drip from becoming a mold job. Put your affected footage into the cost calculator for a planning range, and see the 48-hour mold clock for when DIY drying is enough.
Does insurance pay? The sudden-vs-gradual line
Here's the split that surprises people: homeowners insurance generally covers the water damage from a sudden, accidental leak — the ruined cabinet, flooring and drywall — but not the plumbing repair itself, and not damage from a slow leak that seeped for weeks, which insurers treat as neglected maintenance. An under-sink drip is a common denial for exactly that reason — it's hidden inside a closed cabinet until the floor swells, so by the time it shows it reads as gradual. Protect yourself: photograph the failed part and the damage before you clean up, keep every mitigation receipt (emergency drying is reimbursable while a claim is open), and run your scenario through the claim estimator. Our full coverage guide lays out every water scenario and the denial reasons in one table.
Preventing the next one
Under-sink leaks are among the most preventable water losses. Swap old rubber or plastic supply lines for braided stainless-steel hoses, which fail far less often, and replace any angle-stop valve that is stiff or weeping. Snug — don't overtighten — the P-trap slip nuts, and check the disposal's drain-flange gasket if that's the source. Line the cabinet floor with a plastic under-sink mat so a small drip is visible and contained instead of soaking into particle-board, and drop a battery leak-detector alarm in the back corner — it pings your phone or shrieks the moment it gets wet, which is what keeps a cheap drip from becoming a cabinet-and-floor job.
Common questions
I found water under my kitchen sink — what do I do first?
Stop the water, then find where it came from. Reach to the back of the cabinet and turn the two shut-off valves (angle stops) under the sink clockwise to close them — that isolates the faucet and the dishwasher/disposal supply without touching the whole house. If a valve is seized or there's no valve, close the main water shut-off for the house. Then pull everything out of the cabinet, dry the base, and lay down dry paper towel so you can see exactly where fresh water reappears — that tells you whether it's a pressurized supply line (drips even when no one's using the sink), the drain (only wets when you run water), or the disposal. Get air moving on the wet cabinet floor and the wall behind it the same day, because a sink cabinet is an enclosed box that dries slowly and grows mold fast.
Why is there water under my kitchen sink?
There are five usual suspects, and where the water shows up tells you which. A supply-line or angle-stop leak is under pressure, so it drips or sprays continuously even when the sink is off — often from a corroded braided supply hose or a failing shut-off valve. A drain leak (the P-trap, the slip-nut connections, or the tailpiece) only wets the cabinet when water is running down the drain. A garbage-disposal leak usually comes from the drain-flange gasket on top or the split body of an aging disposal. A faucet-base leak seeps down through the deck and runs to the back of the cabinet. And a dishwasher supply or drain hose that connects under the sink can leak there too. Dry the cabinet, lay paper towel, and watch where it wets first.
Is water under the sink clean or contaminated?
It depends on the source, and it decides how the cleanup is priced. Clean supply-line or faucet water is Category 1 (clean) under the IICRC S500 standard (the water-restoration industry rulebook) — the cheapest to dry. Drain, P-trap and dishwasher-drain water is closer to Category 2 'grey water' (significantly contaminated), because it carries food waste and detergent. Garbage-disposal water is grey water too. Grey water costs more to remediate because soaked porous materials — the particle-board cabinet floor, the drywall behind it — usually come out rather than dry. Any water that has sat for days degrades further, so keep skin, kids and pets out of standing sink-cabinet water when in doubt.
Does homeowners insurance cover a leak under the kitchen sink?
It generally covers the water damage from a sudden, accidental leak, not the failed part and not a slow drip. A standard homeowners policy typically pays to dry out and repair what a sudden burst supply line or split hose ruins — the cabinet, the flooring, the drywall — but excludes the plumbing repair itself, and excludes damage from a slow leak that seeped for weeks or months, which insurers treat as neglected maintenance. A drip under a sink is a classic gradual-damage denial because it's hidden inside a closed cabinet until the floor swells or the cabinet base delaminates. Photograph the failed part and the damage before you clean up, keep every drying receipt, and check your policy wording.
How do I stop it from happening again?
Most under-sink leaks are cheap to prevent. Swap old rubber or plastic supply lines for braided stainless-steel hoses, which fail far less often, and replace angle-stop valves that are stiff or weeping. Snug — don't overtighten — the P-trap slip nuts, and check the disposal drain-flange gasket if that's the source. Line the cabinet floor with a plastic under-sink mat so a small drip is visible and contained instead of soaking into particle-board. Best of all, drop a battery leak-detector alarm in the back corner of the cabinet: it pings your phone or shrieks the moment it gets wet, which is what keeps a $2 drip from becoming a cabinet-and-floor job — mold can start within 24–48 hours.
Gear that catches (or prevents) the next under-sink leak
Disclosure: the links below are Amazon affiliate links. If you buy through them, Amazon pays us a small commission. As an Amazon Associate, Restoration Answers earns from qualifying purchases. We only list gear that genuinely helps in these situations, and you're always free to buy the same items anywhere else.
- Braided stainless-steel faucet supply lines - Replaces the rubber/plastic hoses that fail most often — the single best upgrade under the sink.
- Under-sink leak detector alarm - Sits in the back corner and pings your phone (or shrieks) the moment it gets wet — minutes matter for the mold clock.
- Under-sink cabinet mat / liner - Contains a small drip and makes it visible instead of soaking silently into the particle-board floor.
- Quarter-turn angle-stop shut-off valves - Replaces a stiff or weeping old valve so you can actually shut the water off fast next time.
- Cordless wet/dry shop vacuum - Pulls standing water out of the cabinet base and off the floor before it wicks into the cavity.
Keep reading
Sources & methodology
Every published figure on this page comes from the references below. Where we adjust a national figure for local costs we say so and show the multiplier — we never present our own estimate as if it were sourced. Costs are national ranges; your local market, access, and materials move real quotes in both directions.
- IICRC — S500 Standard for Professional Water Damage Restoration (water categories)
- Insurance Information Institute — Homeowners & renters insurance
- HomeGuide — Water Damage Restoration Cost (per sq ft)
- EPA — A Brief Guide to Mold, Moisture and Your Home (24–48 hr)
- CDC — Clean Up Safely After a Disaster (contaminated water)
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This is general information, not insurance, legal, or engineering advice. Estimates are planning ranges, not quotes — always get on-site assessments, and confirm coverage against your own policy wording or with your insurer.