How to Fix Low Water Pressure in a Single Faucet

Before starting any work, you must prevent water from flowing to the faucet. Look under the sink for two small valves, one for the hot water line and one for the cold. Turn the knobs or levers on these shutoff valves clockwise until they are firmly closed. Once closed, turn on the faucet handles to drain any remaining water from the lines. Place a bucket and a towel under the sink to catch any drips during the repair.

The aerator is the small, screened cap on the very tip of the faucet spout. It's the most common cause of low flow. Unscrew it by turning it counter-clockwise. If it's too tight to turn by hand, wrap it with a cloth or painter's tape and use pliers to gently loosen it. Once removed, disassemble the aerator by separating the screen, washer, and housing. Use a small brush, like an old toothbrush, to scrub away any sediment or mineral deposits from the screen. For heavy buildup, soak the parts in a small bowl of white vinegar for 30 minutes, then scrub and rinse thoroughly. Reassemble the aerator and screw it back onto the faucet hand-tight.

After cleaning and reinstalling the aerator, it's time to test. Slowly turn the shutoff valves under the sink counter-clockwise to turn the water back on. Open the faucet handles and check the water flow. If the pressure is restored, your job is complete. If the pressure is still low, the blockage is further up the line. Proceed to turn the water shutoff valves off again to continue diagnosis.

With the water turned off again, use an adjustable wrench to disconnect the hot and cold supply lines from the faucet's inlet shanks. Position the bucket directly under the loose ends of the supply lines. Have a helper assist or carefully reach up and slowly open one shutoff valve at a time, directing the flow from the hose into the bucket. Let it run for a few seconds. This will flush out any debris lodged in the supply line. If the flow from the hose is strong, the line is clear, and the problem is in the faucet cartridge. If the flow is weak, the issue might be the supply line itself or the shutoff valve.

If the supply lines have good pressure, the clog is in the faucet's cartridge(s). For a double-handle faucet, you'll need to remove each handle. This usually involves prying off a decorative cap and removing a screw with a screwdriver. Once the handle is off, use pliers or an adjustable wrench to unscrew the retaining nut holding the cartridge (or stem) in place. Pull the cartridge straight out. You may need to wiggle it gently. Inspect the small inlet ports on the cartridge for debris. Use a small pick or pin to carefully clean them out. You can also flush the cartridge under running water. Apply a thin layer of plumber's grease to the O-rings before reinserting it. If the cartridge is visibly damaged or heavily calcified, it's best to take it to a hardware store to find an exact replacement.

Once the cartridges are cleaned or replaced and reinstalled, reassemble the faucet by reattaching the handles. Reconnect the hot and cold supply lines to the faucet, ensuring they are snug but not overtightened. With the faucet handles in the 'off' position, slowly turn the water back on at the shutoff valves. Check carefully for any leaks around the supply line connections and the base of the handles. If everything is dry, turn on the faucet and test for water pressure. The flow should now be fully restored.