Check under sinks for moisture, stains, swelling, and active drips every few months. Slow leaks under cabinets are easy to miss because the door hides the evidence until the cabinet floor is already damaged.
Quick under sink checklist
- Look for water on the cabinet floor.
- Touch supply valves and connections with a dry paper towel.
- Check the drain trap while water runs.
- Look for swollen particle board or peeling cabinet finish.
- Smell for musty odor.
- Check after using the disposal or dishwasher if they connect there.
Where leaks hide
Common spots include faucet supply connections, shutoff valves, drain slip nuts, garbage disposal connections, dishwasher drain hoses, sprayer hoses, and the back of the cabinet where you rarely look.
How to check without making a mess
- Remove cleaning bottles and storage from the cabinet.
- Dry the area if it's already damp.
- Run cold water, then hot water.
- Fill the sink a little and drain it while watching the trap.
- Use a dry paper towel around each connection to find small drips.
If you see active dripping, shut off the fixture valve if you can do so safely. If the valve leaks or won't turn, call a plumber.
Why small leaks matter
The EPA says common household leaks include dripping faucets and leaking valves, and that household leaks waste large amounts of water nationally. Under sink leaks also damage cabinets quietly because they often drip into storage, not onto the open floor.
Good maintenance rhythm
- Check under sinks every 3 months, after plumbing work, before travel, and any time you notice musty smell, cabinet swelling, or a water bill change.