Quick answer
When one faucet runs weak or sprays unevenly, the most common cause is a clogged aerator, the small screen at the spout tip. If cleaning it does not help, the cartridge or valve inside the faucet may be worn or blocked, or a shutoff valve may be partly closed. If several fixtures are weak, look at supply or pressure instead.
Start by deciding how widespread the problem is
The first question is whether one faucet is weak or the whole house is. Mr. Rooter notes that low pressure at a single faucet usually points to a clogged aerator, a closed valve or a worn cartridge, and that good pressure at other faucets means the fixture itself is the likely problem.
Check a few other taps, both hot and cold. If only one faucet is affected, keep reading. If several fixtures are weak, skip ahead to the section on supply and pressure.
Aerator and screen buildup
The aerator is the small threaded cap at the end of the spout. It holds a mesh screen that mixes air into the stream and catches grit. Bob Vila explains that mineral deposits or iron oxide residue can clog that screen, which reduces flow and makes the spray uneven. Mr. Rooter calls mineral buildup the likely culprit behind clogged aerators.
Debris can also get in after plumbing work or work on a nearby water line. Bob Vila suggests checking and cleaning aerators at least twice a year, and more often after that kind of work. The EPA's lead guidance also lists cleaning faucet aerators regularly as a good habit, because particles can collect there.
How to clean an aerator safely
This is a ten-minute job for most faucets. Work over a towel or with the drain closed so small parts do not fall into the sink.
- Unscrew the aerator by turning it as Bob Vila describes (clockwise, in his instructions). If it will not budge, wrap masking tape around it before using pliers, since the pliers' teeth can mar the finish.
- Take it apart and photograph the pieces first so you can put them back in the same order.
- Clear loose deposits with a fingertip or a toothpick. Avoid sharp tools that could tear the screen.
- Soak the parts in white vinegar for 20 to 30 minutes, then scrub them with an old toothbrush.
- Hold the screen up to the light to check that the holes are open, then rinse, reassemble and thread it back on.
- Run the water and look at the stream. Use a wrench only if water sprays from the side of the aerator.
If the stream is still weak: the cartridge or valve
If the aerator is clean and flow is still poor, Mr. Rooter says the next suspect is a damaged cartridge, which sits deeper in the faucet near the hot and cold controls. Mr. Rooter also suggests removing the aerator and measuring pressure at the spout with a gauge, with a target of about 45 to 55 psi.
A worn or debris-clogged cartridge or valve can restrict flow, make the handle stiff, or leave you with less hot water than cold. Cartridge designs vary by brand and model, so the replacement part has to match the faucet. Before you take anything apart, close the shutoff valves under the sink, and open the faucet to release pressure. If you are not sure what you are looking at, stop there.
Shutoff valves and supply lines under the sink
Each faucet usually has a small shutoff valve for hot and cold under the sink. Mr. Rooter lists a closed valve among the usual causes of low pressure at a single faucet. A valve that was bumped, or that was not opened all the way after a repair, can quietly cut flow.
Open both valves fully and see whether the stream improves. Then look at the flexible supply lines for kinks, and check connections for dampness or corrosion. A kinked line can restrict flow. A corroded or weeping connection is a leak, and it should be repaired before it damages the cabinet. Turn them gently, and stop if one will not move or starts to drip.
What WaterSense flow rates mean
A weak stream is not always a defect. The EPA's WaterSense program sets a maximum flow of 1.5 gallons per minute at 60 psi for bathroom sink faucets, which it describes as at least 30 percent below the federal standard of 2.2 gpm. It also sets a minimum flow of 0.8 gpm at 20 psi, so labeled faucets still perform at lower pressure.
If you replaced an aerator recently, check the gpm marking on the aerator or faucet. A lower rated aerator will deliver less water by design. The EPA tech sheet also describes a quick test for a bathroom faucet: no more than 0.25 gallons, or 32 ounces, should be collected in 10 seconds if it is meeting the 1.5 gpm maximum.
When it points to the supply line or pressure
If several fixtures run weak, or a shower and a toilet refill slowly too, the cause is probably upstream of the faucet. Waypoint Inspection notes that sediment in the water heater or pipes can restrict flow at multiple fixtures, that undersized supply piping can limit flow, and that a hidden leak or the local water supply can also play a part.
Pressure is easy to check with a gauge on an outdoor hose bib. Waypoint Inspection gives a reading of 40 to 60 psi as the expected range with the water on, and Mr. Rooter's faucet-specific target is 45 to 55 psi. Readings far below that, or flow that drops sharply when someone flushes a toilet, deserve a closer look. Check your water utility's notices as well, since work on a main can lower pressure in a whole neighborhood for a while.
When to call Pyper Plumbing
If the aerator is clean, the valves are open and the stream is still weak, a cartridge or valve replacement or a look at the supply line is a reasonable time to bring in a plumber. Pyper handles faucet and fixture repair and replacement, and leak detection and repair when low flow turns out to come with a leak or damp cabinet.
Call promptly if you see water under the sink, a supply line that is bulging or corroded, or a sudden drop in pressure at every fixture at once. Pyper serves Snohomish, Skagit, Whatcom and Island counties, including emergency repair when a supply problem cannot wait.
Common questions
Can I clean an aerator with vinegar?
Yes. Bob Vila recommends soaking the disassembled parts in white vinegar for 20 to 30 minutes, then scrubbing with an old toothbrush. Check your faucet maker's instructions first, because some finishes can be harmed by acids, and rinse everything well before reinstalling.
Why is my faucet weak only on the hot side?
The sources reviewed here do not address hot-only weakness in detail. Sediment in the water heater or hot lines can restrict flow, according to Waypoint Inspection, and a worn cartridge can affect one side. If cleaning the aerator does not help, have a plumber check the hot supply.
Is a low-flow faucet supposed to feel weak?
Not weak, but lower. WaterSense bathroom faucets are rated at 1.5 gpm or less at 60 psi and must still deliver at least 0.8 gpm at 20 psi. A noticeable drop after you changed the aerator may simply reflect its lower rating. Check the gpm marking.
How often should aerators be cleaned?
Bob Vila suggests at least twice a year, and more often after plumbing or water line work. Hard or mineral-rich water, and sediment after repairs, can clog them sooner.
Sources
Facts in this guide come from the following references. Local rules and manufacturer instructions can differ, so follow your utility and your equipment manual.
- How to clean a faucet aerator (Bob Vila)
- Low water pressure at your kitchen sink (Mr. Rooter Plumbing)
- What causes low water pressure in one faucet but not others (Mr. Rooter Plumbing)
- WaterSense bathroom sink faucets tech sheet (U.S. EPA)
- Basic information about lead in drinking water (U.S. EPA)
- Low water pressure: signs and fixes (Waypoint Inspection)
This guide is general information, not a substitute for an on-site inspection. If you smell natural gas, leave the building and call 911 or your gas utility. Pyper does not perform gas line work.
