Low water pressure in only one faucet usually points to a local problem at that fixture, not a whole-house plumbing failure. This article explains the most common causes, simple checks homeowners can make, when the issue may be inside the faucet, and when it is safer to call a plumber.
Quick Answer
If only one faucet has weak flow, the most likely causes are a clogged aerator, a partially closed shutoff valve, mineral buildup, a blocked supply line, or a worn faucet cartridge. Check whether both hot and cold are weak, then clean the aerator and confirm the valves under the sink are fully open.
The fastest first step is to remove and rinse the aerator before assuming there is a larger plumbing problem.
The Question
SinkSideNate64:
My bathroom sink suddenly has much lower water pressure than the rest of the house. The shower, kitchen sink, and outdoor spigot all seem normal. Both hot and cold water come out, but the stream is weak and uneven. What should I check first before I start replacing parts or calling a plumber?
RaleighFixer37:
Start with the aerator, which is the small screen assembly at the end of the faucet spout. It catches grit, pipe scale, and mineral flakes. When it clogs, the water may look weak, crooked, or bubbly even though the plumbing behind it is fine. Unscrew it by hand or with a wrapped wrench, keep track of the small parts, then rinse the screen. If there is white crust, soak it in vinegar for a while and scrub gently with an old toothbrush. Run the faucet briefly while the aerator is off to flush loose debris. If the flow is strong without the aerator, you found the problem.
CopperTrailMia:
Check the shutoff valves under that sink. There are usually two small valves, one for hot and one for cold. Sometimes one gets bumped during cleaning, storage, or a small repair and ends up partly closed. Turn each valve gently clockwise until it stops, then open it counterclockwise fully. Do not force an old valve because brittle stems can leak. If only the hot side is weak or only the cold side is weak, that specific valve or supply line becomes more suspicious. If both sides are weak, the aerator or faucet body is more likely.
OhioWrenchMark:
A useful diagnostic is separating pressure from flow. People often say "pressure" when they mean the amount of water coming out. If the other fixtures are normal, the actual house pressure is probably fine. What you likely have is a local flow restriction. The restriction can be at the aerator, cartridge, supply hose, shutoff valve, or a short section of pipe serving only that faucet. Turn on hot only, then cold only. If both are equally weak, the blockage is probably after the hot and cold mix, such as the spout or aerator. If one side is much worse, look before the mixing point.
MapleHouseLena:
Mineral buildup is common in areas with hard water. It can collect in the aerator, but it can also collect inside the cartridge or small internal passages of a faucet. If cleaning the aerator helps only a little, look up the faucet model and see whether the cartridge can be removed and cleaned or replaced. Cartridges are not all the same, so avoid buying a random part by appearance alone. Take photos before disassembly, shut the water off first, and place a towel over the drain so tiny screws or clips do not disappear.
PrairieSinkGuy:
One thing people overlook is debris after plumbing work. If someone recently replaced a water heater, repaired a pipe, changed a valve, or shut off the main water supply, loose scale can travel to the first narrow screen it reaches. A bathroom faucet aerator is a perfect trap for that debris. In that case, cleaning the aerator may fix it, but you may also want to flush the line by running the faucet briefly with the aerator removed. Use moderate flow and keep a cup or towel ready, because water can splash when the aerator is off.
SuburbanDana18:
If the faucet has flexible supply hoses, one of them may be kinked, pinched, or internally blocked. This can happen when a vanity item is pushed against the hose or after someone moves the faucet connection during a repair. Look under the sink with a flashlight and make sure the hoses have smooth curves rather than sharp bends. If the weak flow is only on hot or only on cold, the matching supply hose is a reasonable suspect. Replacing a supply line is usually not expensive, but the shutoff valve must work properly first.
HarborHomeCaleb:
For a single-handle faucet, the cartridge is a common cause when both temperature and flow feel odd. A worn or clogged cartridge can reduce flow, make temperature control inconsistent, or cause the handle to feel stiff. Cleaning the aerator is still the first check because it is simple, but the cartridge is next if the aerator is clean and the supply valves are open. Some cartridges pull out easily, while others need a specific retaining clip or puller. That is where reading the manufacturer instructions matters because forcing parts can damage the faucet body.
BluegrassReno22:
Think about whether the problem appeared suddenly or slowly. Sudden low flow often means debris, a moved valve, or a kinked hose. Slow decline over months usually points to mineral scale, corrosion, or a cartridge getting clogged. If the house has older galvanized pipes, one branch line can become restricted while other fixtures still seem okay. That is less common than an aerator clog, but it is possible in older homes. If you remove the aerator and still get weak flow from both hot and cold, the issue may be deeper than the faucet tip.
DesertValveKim:
There is also a cost angle. Cleaning an aerator costs almost nothing. Replacing an aerator is usually inexpensive. A cartridge may cost more, and a plumber visit costs more still. So it makes sense to work from easiest to hardest: aerator, shutoff valves, visible hose kink, hot-versus-cold test, then cartridge or supply line. The mistake is starting with the most expensive explanation first. A single weak faucet is usually a small restriction until proven otherwise.
NorthForkJules:
Call someone if you see leaking shutoff valves, corrosion, wet cabinet flooring, a valve that will not close, or a faucet that gets worse after you try to work on it. Basic checks are fine for many homeowners, but water damage can become expensive quickly. Also, if the faucet is on a second floor or above finished space, be extra cautious. A low-flow problem is annoying, but a rushed repair that creates a leak is worse. Know where the main water shutoff is before loosening any supply connection.
Key Points to Consider
Main Point
When only one faucet has low flow, the issue is usually local to that fixture rather than the whole plumbing system.
Best Next Step
Remove the aerator, clean it, and test the faucet briefly without it to see whether normal flow returns.
Common Mistake
Do not assume the water main, city supply, or pressure regulator is failing when every other fixture works normally.
Testing hot and cold separately helps narrow the problem to the aerator, cartridge, valve, hose, or branch line.
What the Responses Suggest
The most useful shared conclusion is that one weak faucet should be diagnosed from the faucet outward. A clogged aerator is the most common and simplest explanation, especially when the stream is uneven or sprays sideways. A partially closed shutoff valve, kinked supply line, or clogged cartridge can create a similar symptom.
Some suggestions are broadly useful for almost any homeowner, such as comparing hot and cold flow, checking whether other fixtures are normal, and looking under the sink for obvious valve or hose issues. Other suggestions depend on the faucet design, the age of the plumbing, local water hardness, and whether any recent repair work stirred up debris.
Separate subjective perspectives from reliable factual information. A personal repair story may point you in a useful direction, but the stronger approach is to test one likely cause at a time and stop if the repair moves beyond your comfort level.
Common Mistakes and Important Limitations
A common mistake is replacing the entire faucet before checking the aerator. Another mistake is forcing old shutoff valves or faucet parts. Older valves can leak when disturbed, and some cartridges require a specific removal method. Low flow can also be caused by pipe corrosion or a blocked branch line, which is harder to confirm without disconnecting lines or measuring flow.
To avoid the most common mistake, test the faucet with the aerator removed before buying parts. If the stream becomes strong, clean or replace the aerator. If the stream is still weak, compare hot and cold, inspect the valves, and consider the cartridge or supply lines next.
Shut off the water before loosening any faucet, valve, cartridge, or supply-line connection.
A Simple Example
A homeowner notices that the bathroom faucet has a weak stream, but the shower and kitchen sink are normal. First, they turn on cold only, then hot only, and both are weak. That suggests the restriction may be after the water mixes. They unscrew the aerator and find small white mineral flakes in the screen. With the aerator removed, the faucet runs strongly. After rinsing and soaking the aerator, the flow returns to normal. In this example, the problem was not the house pressure, the water company, or a hidden leak. It was a clogged screen at the end of one faucet.
Frequently Asked Questions
What is the clearest answer to What Causes Low Water Pressure in Only One Faucet??
The clearest answer is that the faucet likely has a local restriction. The most common starting points are a clogged aerator, a partly closed shutoff valve, a kinked supply hose, mineral buildup, or a clogged cartridge.
Does the answer depend on individual circumstances?
Yes. The likely cause depends on whether hot, cold, or both sides are weak; whether the issue appeared suddenly or gradually; the age of the faucet; local water hardness; and whether plumbing work was done recently.
What should someone in the United States check first?
For a typical U.S. bathroom or kitchen faucet, check the aerator first because many faucets have removable aerator screens. Then confirm that the under-sink shutoff valves are fully open and not leaking.
Where can important information be verified?
For model-specific repair steps, check the faucet manufacturer's instructions. For leaks, old valves, pipe corrosion, or work that requires disconnecting supply lines, a licensed local plumber is the appropriate source.