Start by checking the aerator and shutoff valve
Low water pressure at your bathroom sink usually comes from one of two places: a clogged aerator (the screen at the faucet tip) or a partially closed shutoff valve under the sink. The aerator is the fastest fix—it takes two minutes and costs nothing if you already have the part.
Unscrew the aerator by turning it counterclockwise by hand. If you cannot grip it, wrap a cloth around it for traction. Hold it up to the light. If you see mineral buildup, rust, or debris blocking the holes, that is your problem. Rinse it under hot water and use an old toothbrush to scrub away deposits. If the screen is damaged or heavily corroded, you can buy a replacement aerator for $3 to $8 at any hardware store—bring the old one to match the size.
While you have the cabinet open, locate the shutoff valve on the water line behind the sink. It looks like a small knob or lever. Turn it fully counterclockwise (or pull the lever all the way out if it is a ball valve). If it was partially closed, this alone may restore your pressure. If the valve is stuck or will not turn, do not force it—a stuck valve often means it needs replacement, which requires a plumber.
Key Takeaways
- An aerator clogged with mineral deposits is the most common cause of low sink pressure and can be cleaned in two minutes with a toothbrush and hot water.
- Check the shutoff valve under your sink and make sure it is turned fully open—a partially closed valve cuts pressure without any other sign of trouble.
- If both the aerator and shutoff valve are clear and open, the problem likely exists in the main water line or supply, and you will need a plumber to diagnose it.
- Replacing an aerator costs $3 to $8 and takes one minute; cleaning a clogged one costs nothing and takes two minutes.
- Hard water areas see aerator clogs more often, so plan to clean yours every six months if you live in a high-mineral region.
Clean mineral deposits from the aerator
Mineral buildup is the reason aerators clog. In areas with hard water, calcium and magnesium deposits accumulate inside the aerator screen and restrict flow. The fix is straightforward: soak the aerator in white vinegar for 30 minutes to an hour, then scrub it with an old toothbrush.
Fill a small cup or bowl with white vinegar and submerge the aerator completely. Let it sit for at least 30 minutes—overnight works even better for heavy buildup. After soaking, use the toothbrush to scrub the screen and the inside of the aerator body. Pay attention to the tiny holes in the screen; use the brush bristles to poke through each one. Rinse under hot running water and screw the aerator back onto the faucet.
Turn on the sink and check the pressure. If it has improved but is still weak, soak the aerator again for another hour. If pressure is now normal, you are done. If pressure is still low after two soaks, the aerator screen may be damaged and need replacement.
Replace the aerator if cleaning does not work
If soaking and scrubbing do not restore pressure, the aerator screen is likely corroded or the internal parts are worn. Replacement aerators are inexpensive and take 30 seconds to install. Bring your old aerator to the hardware store to match the thread size—most bathroom sink aerators are standard, but a few older faucets use different sizes.
Unscrew the old aerator and screw the new one on by hand until it is snug. Do not overtighten—hand-tight is enough. Turn on the water and test the pressure. A new aerator should restore flow to normal unless the problem is deeper in the supply line.
Inspect the shutoff valve and supply lines
If the aerator is clean and the shutoff valve is fully open but pressure is still low, the problem is in the water supply line itself. This is where a plumber becomes necessary, because the issue could be a kink in the flexible supply line, a partially blocked main shutoff valve, or sediment in the line.
Before calling a plumber, check the flexible supply lines under the sink. They are usually braided metal or plastic tubes that run from the shutoff valve to the faucet. Look for kinks, cracks, or obvious damage. If a line is kinked, straighten it gently. If it is cracked or leaking, it needs replacement—this is a $15 to $30 part and a 10-minute job for a plumber.
If the supply lines look fine, the issue is likely in the main water line or the shutoff valve itself is partially blocked internally. At this point, contact a plumber. They can test the pressure at different points and identify whether the problem is in your home's plumbing or with the water supply from the street.
Check for leaks that reduce pressure
A leak elsewhere in your home can reduce pressure at a single sink or throughout the house. If only your bathroom sink has low pressure, a leak is less likely—but if multiple fixtures are weak, check for dripping faucets, running toilets, or wet spots under sinks and in the basement.
Listen for running water when all faucets are off. If you hear water flowing, you have a leak. Check under the sink, in the basement, and around the water heater. Even a small leak wastes water and reduces pressure. If you find a leak, tighten the connection or replace the part. If you cannot locate the leak but suspect one, a plumber can use a pressure gauge to confirm.
Know when to call a plumber
Call a plumber if the aerator is clean, the shutoff valve is fully open, and pressure is still low. Also call if the shutoff valve is stuck and will not turn, or if you see water leaking from the supply line or valve. A plumber can diagnose whether the problem is in your home's plumbing or in the main water line, and they have tools to test pressure and identify blockages.
Most plumbers charge $100 to $200 for a service call and diagnosis. If the fix is straightforward—like replacing a supply line or clearing a blocked valve—the total cost is usually $150 to $300. If the problem is in the main line or requires more extensive work, costs vary widely depending on what is found.
Prevent future aerator clogs
In hard water areas, aerators clog regularly. Clean yours every six months to avoid pressure drops. Set a reminder on your phone or calendar. The job takes five minutes and costs nothing.
If you travel or leave your home empty for weeks, mineral deposits can build up faster. When you return, clean the aerator before you notice a pressure drop. Some people install a water softener to reduce mineral content throughout the house, which prevents clogs in aerators, showerheads, and appliances—but a softener is a larger investment and requires maintenance.
Frequently Asked Questions
Why is only one sink low pressure and not the others?
A clogged aerator affects only that faucet. If multiple sinks or fixtures are weak, the problem is in the main water line or a shutoff valve. If only one sink is affected, start by cleaning the aerator—that solves the problem 80 percent of the time.
Can I clean the aerator without removing it?
No. You need to unscrew it to soak it in vinegar and scrub the screen. Soaking it in place does not work because the vinegar cannot reach the inside of the screen. Unscrewing takes 10 seconds, so it is worth doing.
What if the aerator is stuck and I cannot unscrew it?
Wrap a cloth around it for grip and try again. If it still will not budge, soak the base in vinegar for 15 minutes to loosen mineral deposits, then try again. If it remains stuck, a plumber can remove it without damaging the faucet.
How do I know if my shutoff valve is fully open?
A ball valve (lever-style) is open when the lever points in line with the pipe. A gate valve (knob-style) is open when the knob turns fully counterclockwise and stops. If you cannot turn it further, it is open. If you can still turn it, keep going until it stops.
Is low water pressure a sign of a bigger problem?
Usually not. A clogged aerator is the cause 80 percent of the time. If multiple fixtures are weak, check for leaks. If no leak exists and pressure is still low everywhere, the issue may be with your water supplier or the main shutoff valve, and you should contact your water company or a plumber.