Tired of Wet Cabinets? How to Permanently Fix Leaks Under the Kitchen Sink

Dealing with a leaky sink can be incredibly frustrating. The constant dripping leads to water damage under your kitchen cabinetry, not to mention the mold risks if left unaddressed. But many types of leaks originating under the kitchen sink are totally repairable without calling an expensive plumber. With a few basic tools and following this guide, you can diagnose the leak source accurately, fix it yourself, and prevent future wet cabinet headaches.

Kitchen sink leaks typically occur due to worn washers or loose connections in the faucet, supply lines, P-trap, or drain tailpiece. Thankfully, most under-sink plumbing uses slip joints and connections that can be tightened and resealed without soldering. If you notice water pooling under your sink or dripping down cabinetry when the faucet runs, don't panic. Just follow these steps to permanently solve the problem.

Finding the Exact Leak Source

Figuring out the specific location where the water is coming from is crucial for fixing an under sink leak properly. Inspect with the faucet on and off to isolate whether it's coming from the faucet itself, the drain plumbing, or supply line connections.

Inspect with Faucet On

Turn on your kitchen faucet and let the water run. Get under the sink and watch the pipes and surrounding area closely. Drips originating near the faucet spout indicate a leak in the faucet seals or connections. Water on the straight or curved drain pipes signals the leak is somewhere in the drainage system.

Check where the supply lines connect to the sink tailpieces and shutoff valves too. If you see water beading at those connections, you've identified the problem area.

Check Supply Line Connections

With the faucet off, take a close look at where the flexible supply tubes connect. The leak may be coming from worn washers or cracked tube nuts at the joints. Examine the supply tubing for punctures too. Even minor drips here will leak steadily.

Shutting Off the Water Supply

Before starting repairs, you'll need to stop the flow of water to prevent further leaking while you work. There are a couple ways to do this depending on your setup.

Close Sink Shutoff Valves

Most modern sinks have shutoff valves mounted to the cabinet wall behind the sink. Look for two knobs about a quarter-turn past vertical - these control hot and cold water. Turn them clockwise to shut off both completely.

Main House Valve

If your sink lacks individual shutoff valves, locate the main water supply shutoff for your house. It's typically near the front exterior wall or water meter. Rotate it clockwise to shut off water to the entire home until the leak repair is complete.

Draining the Pipes

With the water supply stopped, place a bucket beneath the sink drain. Open the faucet to allow any water remaining in the drain pipes to empty out via gravity into the bucket. This prevents spills during disassembly.

Disassembling Under the Sink

Accessing the leaky components requires partially detaching the drain P-trap and supply tubes. Don't be intimidated - these connections are designed for easy assembly/disassembly during repairs.

Removing the P-Trap

The curved P-trap piece connects to the sink tailpiece via slip joints - rings with a sliding sleeve to tighten them. Loosen the rings by hand or with pliers and slide the P-trap off, allowing remaining water to drain into the bucket.

Detaching the Tailpiece

The tailpiece is the straight length of pipe coming down from the sink opening. Loosen the slip nut connecting it to the sink with pliers and slide the tailpiece off the sink stub out.

Supply Line Nuts

Use an adjustable wrench to detach the supply lines from the shutoff valves and faucet connections by unscrewing the tube nuts. Again, allow water to drain before fully removing.

Pinpointing the Exact Leak Spot

With full access, inspect each component for the source of the drip. Leaks most often occur at slip joints and deteriorated washers. Thoroughly examining the disassembled pipes helps pinpoint the exact problem spot.

Check Joints and Washers

Focus on areas where pipe segments meet - the washers inside these joints wear over time. Leaky P-traps and loosened slip nuts at the sink stub out are very common. Replace any worn out rubber washers.

Supply Line Issues

Examine the supply tubing and shutoff valves closely. Cracked pipe, punctured supply hoses, and valve corrosion can all cause drips. Replace damaged supply components as needed.

Cleaning and Re-Sealing the Problem Area

Once you’ve found the leak source, thoroughly clean and prepare the area for re-sealing. This helps create a watertight connection.

Clean Surfaces

Use towels or rags to absorb standing water and wipe the area clean of grime. For mineral deposits on metal pipes/valves, scrub with steel wool.

Sealing Materials

Apply plumber's putty around the base of the faucet. Use Teflon tape to seal threaded supply line connections. Spread pipe joint compound on slip joint threads before reassembling.

Reassembling the Sink Plumbing

After sealing the leak location, reattach the pipes and supply lines in reverse order of how you detached them. Hand tighten slip joints fully then add a quarter turn with pliers to lock them in place.

Reconnect Drain Pipes

Slide the tailpiece and P-trap back onto their slip fittings, aligning them properly without overtightening. Replace washers if necessary.

Reattach Supply Lines

Screw the flexible supply tubes back into the faucet and shutoff valves using a wrench. Take care not to pinch the tubing.

Turning Water Supply Back On

With everything reassembled properly, slowly turn your shutoff valves counterclockwise to restore water flow. Immediately check below for any continued dripping and address if so. Leaving valves partially closed allows you to fine tune any minor leaks as pressure increases before fully opening.

The moment of truth - turn your faucet on and off and let the water run for several minutes. Get under the sink to verify no drips appear at joints as the pipes pressurize. Never use a newly-repaired sink without checking thoroughly.

By methodically approaching under sink leak diagnosis and following these steps, you can permanently solve the problem yourself. Proper sealing and tightening slip joints during reassembly prevents future leakage. Monitor your plumbing periodically and act quickly if new drips ever occur to prevent water damage.