Quick Answer:
If only one bathroom sink has weak flow, the cause is usually local to that fixture: a clogged aerator, debris in the short supply line, or a partially closed or failing angle stop valve. Start by cleaning the aerator, flushing the supply line, and inspecting the angle stop before calling a plumber.
Why This Happens
When other taps in the house are fine, the problem is almost always at or immediately before the faucet. Common reasons:
- Mineral buildup or tiny debris trapped in the aerator.
- Sediment or a small obstruction inside the flexible supply line or the valve screen.
- A partially closed or corroded angle stop valve that isn’t allowing full flow.
- Internal cartridge or valve components inside the faucet that are clogged or worn.
Symptoms you might notice alongside low flow include difficulty moving the handle; you might also see a faucet handle hard to turn or brief bursts of air and sputtering when you reopen the water, similar to a sink sputters after shutoff situation. Those are clues to check the same local parts listed above.
Step-by-Step What to Do
1. Confirm the problem is only this sink
- Turn on another nearby faucet (shower or another sink). If their pressure is normal, the issue is local to this fixture.
- Shut off both hot and cold at the faucet and prepare to work on this sink only.
2. Clean the aerator
- Close the drain or use a sink plug so small parts don’t fall in.
- Unscrew the aerator at the tip of the spout. If it’s tight, wrap the aerator with a cloth and use pliers gently to avoid scratching.
- Disassemble the aerator parts, rinse, and remove deposits with an old toothbrush. Soak in white vinegar for 15–30 minutes if mineral scale is heavy, then rinse and reassemble.
- Test the water. If flow improves, you’ve likely fixed it.
3. Flush the supply line
- Under the sink, locate the angle stop(s) for hot and cold. Put a bucket under the connection to catch water and debris.
- Turn the angle stop off, then disconnect the flexible supply line at the valve end (use two wrenches to avoid twisting fittings). Be ready for water in the line.
- With the supply line disconnected, briefly open the valve to flush any debris into the bucket, then close it again.
- Inspect the end of the supply line and the valve opening for grit. Reconnect securely and test the faucet.
4. Inspect the angle stop valve
- Make sure the valve is fully open (turn clockwise to close, counterclockwise to open for most valves). If it was partly closed, opening it fully often restores normal flow.
- Move the valve handle gently a few times to clear light corrosion or mineral build-up. If the handle is stiff or leaks, the valve may need replacement.
- If you see signs of corrosion, heavy scale, or persistent leaks from the valve body, note this for the repair or replacement step.
5. Check faucet internals and test
- If cleaning the aerator and flushing the supply line didn’t fix it, the faucet cartridge or internal valve may be clogged. Follow the manufacturer’s guide to remove and inspect the cartridge or cartridge assembly.
- After any cleaning or reassembly, turn on the angle stop(s) slowly and check flow and leaks.
What Not to Do
- Do not rush to replace the main shutoff valve for the house. This is rarely the cause when only one sink is affected and can lead to unnecessary work and expense.
- Do not force a stuck angle stop with excessive force; you can break the valve or the threaded fitting. If it won’t move, stop and get professional help.
- Avoid overtightening the aerator or supply-line fittings—tighten snugly but not excessively to prevent damage.
When to Call a Professional
- You’ve cleaned the aerator, flushed the line, and inspected the valve but the pressure is still low.
- The angle stop is corroded, leaking, or completely stuck and won’t operate.
- You find internal faucet damage or the cartridge is broken and you’re uncomfortable replacing it yourself.
- Multiple attempts to clear debris keep failing or you see unusual corrosion that suggests a larger plumbing issue.
Safety Notes
- Always shut off the angle stop(s) before disconnecting supply lines. If an angle stop won’t shut off, be prepared to close the house main only if you know how and must stop a leak—otherwise call a pro.
- Beware of hot water. If you’ll be working on the hot supply, open the tap briefly to cool the line before disconnecting.
- Use a bucket and towels to avoid water damage. Protect chrome and fixtures with a cloth when using pliers.
- Wear eye protection when flushing lines—debris can spray unexpectedly.
Common Homeowner Questions
- Why is only this sink affected?
Because the clog or restriction is located at the aerator, the supply line, the angle stop, or inside the faucet itself—parts specific to that fixture. - How do I remove a stuck aerator?
Wrap it with a cloth and use pliers gently; if it’s corroded, apply a little penetrating oil and let it sit before trying again. - Will I need a plumber?
If basic cleaning and flushing don’t work, or if valves are corroded or leaking, call a plumber for repairs or valve replacement.