Drip from behind the handle
The area around the stem or packing nut gets wet first, then water runs down the valve body.
Start here: Start with the stem packing check. A small snug on the packing nut often stops this type of seep.
Plumbing
Under Sink Shutoff Valve Dripping
Direct answer: An under sink shutoff valve usually drips from one of three places: the handle stem, the compression connection to the pipe, or the outlet where the supply line attaches. Start by drying everything and finding the first wet spot, because the lowest drip is often not the real source.
Most likely: Most often, the leak is a slightly loose packing nut behind the handle or a seep at the supply line connection, especially after the valve has been turned recently.
Under-sink leaks like to fool people. Water runs down the valve, along the tubing, and drops from the lowest point. Dry it first, watch it under pressure, and separate a stem leak from a connection leak before you touch anything. Reality check: a valve that only drips after you turn it is often worn, even if it looks fine sitting still. Common wrong move: tightening the handle screw when the leak is actually coming from the packing nut behind the handle.
Don’t start with: Do not start by buying a new valve or cranking hard on every nut. Overtightening can split an old ferrule, distort a supply line seal, or turn a small seep into a full leak.
If the drip starts behind the handleSnug the shutoff valve packing nut slightly and recheck.
If the drip starts at the outlet to the faucet supply tubeInspect the under sink shutoff valve supply line connection before blaming the valve body.
Last reviewed: 2026-04-05
What kind of under-sink shutoff valve drip do you have?
Drip at the top outlet nut
Water forms where the faucet supply line connects to the shutoff valve outlet.
Start here: Check whether the supply line nut is loose, cross-threaded, or leaking from its seal.
Drip at the wall side of the valve
The back of the valve near the pipe coming out of the wall gets wet first.
Start here: Look closely at the compression connection. If that joint is the first wet point, simple tightening may or may not save it.
Valve only leaks after you turn it
It stays dry untouched, but starts seeping after opening or closing the valve.
Start here: That usually points to worn stem packing or an aging valve that no longer seals well after being disturbed.
Most likely causes
1. Loose shutoff valve packing nut
A drip from right behind the handle is the classic sign, especially on older multi-turn valves.
Quick check: Dry the stem area, open the faucet, then watch for moisture forming around the nut just behind the handle.
2. Leaking under sink shutoff valve supply line connection
If the first wet point is at the outlet where the faucet supply line attaches, the connection or line seal is more likely than the valve body.
Quick check: Wrap the stem area dry, then watch the outlet nut while the faucet runs and again after it shuts off.
3. Seeping shutoff valve compression connection at the wall stub-out
Water at the back of the valve usually means the compression nut or ferrule connection is leaking.
Quick check: Dry the pipe and valve back side completely and look for a fresh bead forming where the valve meets the pipe.
4. Worn or cracked under sink angle stop valve
If the valve body itself seeps, or tightening the packing nut and outlet connection does nothing, the valve is usually at the end of its life.
Quick check: Look for moisture from the casting, corrosion around the body, or a leak that returns quickly after careful tightening.
Step-by-step fix
Step 1: Dry the area and find the first wet point
You need the source, not the final drip. Under-sink leaks travel along metal and tubing before they fall.
- Place a small container or towel under the valve so you can work without soaking the cabinet.
- Dry the shutoff valve, the pipe coming from the wall, and the faucet supply line with a rag or paper towel.
- Turn the faucet on and off a few times while watching closely with a flashlight.
- Touch a dry paper towel to three spots separately: behind the handle, at the top outlet connection, and at the wall-side connection.
- Mark the first spot that turns wet.
Next move: You now know whether this is a stem leak, outlet connection leak, wall-side compression leak, or a valve body leak. If everything gets wet too fast to tell, shut the valve if it will close, dry it again, and watch during one slow reopen. If it still floods immediately, treat it as a failing valve and prepare to shut off the house water.
What to conclude: The first wet point tells you where to act. Most bad guesses happen because people chase the drip instead of the source.
Stop if:
- Water is spraying instead of dripping.
- The cabinet, wall, or floor is already swelling or stained from ongoing leakage.
- You cannot identify the source without forcing the valve or moving rigid piping.
Step 2: Check the packing nut behind the handle first
A stem seep is common, low-risk to test, and often fixable without replacing the valve.
- Look just behind the handle for a small hex packing nut around the valve stem.
- Hold the valve body steady with one wrench if needed.
- Turn the packing nut clockwise only about one-eighth to one-quarter turn.
- Open and close the valve gently, then watch the stem area for a few minutes.
- If the valve gets harder to turn, stop tightening.
Next move: If the stem area stays dry, the leak was loose packing and you can leave the valve in service. If the stem still seeps after a small adjustment, or the valve becomes very stiff, the stem packing or valve is worn and replacement is the better fix.
What to conclude: A slight snug can compress old packing enough to stop a drip. More force usually does not help for long.
Step 3: Check the faucet supply line connection at the valve outlet
A leak at the top outlet is often the supply line connection, not the shutoff valve itself.
- Dry the outlet nut and the lower end of the faucet supply line.
- Use one wrench to hold the shutoff valve body and another to snug the supply line nut slightly.
- Do not reef on it; a small turn is enough for a test.
- Run the faucet and then shut it off while watching the outlet connection.
- If the connection still wets immediately, inspect the supply line for kinks, corrosion, or a damaged sealing end.
Next move: If the outlet stays dry after a slight snug, the connection was loose. If the leak continues only at that outlet and the line looks damaged or has been reused several times, replace the under sink shutoff valve supply line first. If a new line still leaks there, the valve outlet seat is likely damaged and the valve should be replaced.
Step 4: Inspect the wall-side compression connection and the valve body
If the back of the valve is the first wet point, you need to separate a tired compression joint from a valve body that is done.
- Dry the pipe stub-out and the back side of the valve completely.
- Watch for a bead forming at the compression nut where the valve meets the pipe.
- If that exact joint is wet first, hold the valve body steady and try a very small snug on the compression nut.
- If moisture appears from the valve casting, around a crack, or from multiple points, stop trying to tighten it.
- Plan on replacing the under sink angle stop valve if the body leaks or the compression joint will not stop with a careful minor adjustment.
Next move: If a tiny snug stops a slow seep at the compression nut, monitor it closely over the next day. If the joint still leaks, the ferrule may be damaged or the valve may be failing. At that point, valve replacement is the realistic repair.
Step 5: Replace the failed part or shut down and call for help
Once the leak source is clear, the right repair is usually straightforward: supply line if the outlet seal is bad, valve if the stem or body is worn.
- If the leak is only at the outlet and the supply line is damaged or still leaks after careful tightening, replace the under sink shutoff valve supply line.
- If the leak is from the stem after a small packing nut adjustment, or from the valve body or wall-side connection that will not stabilize, replace the under sink angle stop valve.
- Before replacing a valve, confirm you can shut off water upstream and that the old valve can be removed without stressing the pipe in the wall.
- If you cannot isolate water safely, or the stub-out pipe is fragile, corroded, or short, stop and call a plumber.
- After repair, dry the area fully and recheck with the faucet on, off, and after ten minutes of sitting under pressure.
A good result: The valve and nearby connections stay dry during use and while sitting still.
If not: If a new supply line still leaks at the valve outlet, or a replacement valve connection seeps at the wall, shut the water back off and correct the installation before restoring normal use.
What to conclude: At this point you are past guesswork. Replace only the part that matches the leak source you confirmed.
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FAQ
Can I just tighten a dripping under-sink shutoff valve?
Sometimes, yes, but only a little and only after you know where the leak starts. A small snug on the packing nut can stop a stem seep. A slight snug on the supply line nut can stop a loose outlet connection. If the valve body leaks or the connection keeps seeping, tightening harder usually makes things worse.
Why does the shutoff valve drip only after I turn it?
That usually means the stem packing was disturbed and no longer seals well, or the valve is simply worn out. Older valves often sit dry for years, then start leaking the first time they are operated.
Is the leak coming from the valve or the faucet supply line?
Dry both completely and watch for the first wet point. If moisture starts right at the top outlet nut, suspect the faucet supply line connection first. If it starts behind the handle, suspect the packing nut or valve stem. If it starts at the back near the wall, suspect the compression connection or the valve body.
Should I replace the supply line before replacing the shutoff valve?
If the leak is clearly isolated to the outlet connection and the line looks kinked, corroded, or has a damaged sealing end, replacing the supply line first is reasonable. If the stem leaks, the body leaks, or the wall-side connection will not stabilize, the valve itself is the better target.
When should I call a plumber for a dripping shutoff valve?
Call if the valve will not close, the pipe in the wall moves, corrosion is heavy, the leak is more than a slow drip, or you are not confident shutting off water upstream. Also call if the valve is on fragile rigid piping and you cannot support it safely during removal.