Low Water Pressure in Only One Faucet? Check These 4 Things

Graphic: summary of this guide, made by our team from the cited sources.

First, make sure it really is just one faucet

Portland Water Bureau says to check every faucet, inside and outside, and to compare hot and cold water (Portland Water Bureau). What you find tells you where to look:

What you see	Where the problem likely is
One faucet weak, hot and cold both	That faucet's aerator or cartridge, or both shutoff valves
One faucet weak, only hot or only cold	That side's shutoff valve, supply line or cartridge
Hot water weak at every faucet, cold fine	Portland says to examine your water heater for leaks or other failures (Portland Water Bureau)
Every faucet weak, including outdoor spigots	Whole-house pressure: see "When it is not just one faucet" below

The 4 checks, in order

1. Clean the aerator

The aerator is the small screen at the tip of the spout. Sediment and mineral bits collect there. For both kitchen and bathroom faucets, Moen says to remove the aerator and rinse off any debris. Close the sink drain first so small parts cannot fall in. Unscrew the aerator by hand or with pliers wrapped in a cloth, rinse the screen, and run the faucet for a few seconds without it.

If the flow is strong without the aerator, the aerator was the problem. Clean it or replace it.

2. Check the pull-down or side sprayer

On pull-down and pull-out kitchen faucets, Moen says to check the hose and its screen. If the flow is low even from the hose, the cartridge likely needs to be replaced (Moen). GROHE's test for pull-down faucets is quick: unthread the spray head from the hose (clip the hose so it can't slide back into the spout) and run the water. If the flow improves with the head off, the head is the problem; GROHE suggests cleaning the aerator or soaking the spray head in a 50/50 mix of water and white vinegar (GROHE). On faucets with a separate side sprayer, Moen lists a stuck diverter as a possible cause (Moen).

3. Open the shutoff valves under the sink

Look under the sink for the two small valves where the supply lines start. They are sometimes left partly closed after a repair. Moen recommends checking that the supply lines from the shutoff valves give the faucet full pressure from both hot and cold. Turn each valve fully counterclockwise. Do not force a valve that is stuck. Old valves can start to leak when moved.

4. Clean or replace the cartridge

If the aerator and valves are fine, the cartridge inside the faucet body may have debris in it. Moen says the cartridge (one for single-handle faucets, two for two-handle faucets) would need to be replaced and the valve body flushed and cleaned (Moen). Turn off both shutoff valves before taking the handle off, and take the old cartridge to the store to match it.

Cartridge or supply line? The cartridge-out test

If a new or clean cartridge didn't help, this test tells you whether to keep working on the faucet or look under the sink. GROHE describes it: with the supply turned off, remove the cartridge, then slowly turn the water back on at the side that was weak. Strong flow with the cartridge out means the cartridge was the restriction. Still weak with the cartridge out means the supply line is collapsed or blocked (GROHE). Hold a towel over the faucet body and open the valve only a little; water comes straight up.

Result with cartridge removed	What it means	Next step
Strong flow	Cartridge was blocking flow	Install a matching new cartridge
Still weak	Supply line or shutoff valve	Replace the braided supply line or call a plumber for the valve

Did the faucet just get a new aerator?

Some low flow is by design. EPA WaterSense says a bathroom aerator or faucet rated at 1.5 gallons per minute can cut a sink's flow by 30 percent or more from the standard 2.2 gallons per minute (EPA WaterSense). If the flow is steady but lower than you are used to, that may be the rating, not a clog.

When it is not just one faucet

If every fixture is weak, look at the whole house. EPA WaterSense says fixtures work best when incoming water pressure is between 45 and 60 psi, and that pressure much lower than 45 psi may mean a leak in the home (EPA WaterSense). Portland Water Bureau says plumbing code requires a pressure reducing valve if your home receives higher than 80 psi (Portland Water Bureau). A licensed plumber can test pressure and check the main shutoff and pressure reducing valve.

When to call a plumber

• The shutoff valve under the sink will not turn, or it leaks when you move it.
• A new cartridge and a clean aerator did not bring the flow back.
• The weak flow also shows up at a nearby fixture, which points to the pipe, not the faucet.
• You see water under the sink or stains on the cabinet floor.