The first and most common cause of low pressure in a single faucet is a clogged aerator or sprayer head. Mineral deposits (scale) and small debris can build up over time and restrict water flow. Begin by turning off the hot and cold water supply valves located under the sink. Turn the handles clockwise until they are fully closed. Then, turn the faucet handle on to relieve any remaining pressure and confirm the water is off. Carefully unscrew the pull-down sprayer head from the hose. Most can be unscrewed by hand, but if it is tight, wrap a rag around it and use channel-lock pliers to gently loosen it. Once removed, look inside the sprayer head and at the screen on the end of the hose for any visible debris.

With the sprayer head removed, prepare a small bowl with enough white vinegar to fully submerge it. Place the sprayer head in the bowl and let it soak for at least one hour (or overnight for heavy buildup). The acetic acid in the vinegar will dissolve the mineral deposits. While it soaks, use a small brush, like an old toothbrush, to gently scrub the nozzle holes and the inlet screen to dislodge any remaining debris. After soaking, rinse the sprayer head thoroughly with warm water, both inside and out. To test if the clog was in the head, place the end of the sprayer hose in a bucket and slowly turn on the water valves. If you have strong pressure from the hose, the clog was in the sprayer head.

If cleaning the sprayer head did not solve the issue, the problem may be a clogged faucet cartridge. Ensure the water is still off. Locate the set screw that holds the faucet handle in place, which is often hidden under a small decorative cap (hot/cold indicator) or at the base of the handle. Use a small flathead screwdriver to pry off the cap, and an Allen wrench or Phillips screwdriver to loosen the set screw and remove the handle. Next, unscrew the decorative dome cap covering the cartridge, then use channel-lock pliers to unscrew the retaining nut holding the cartridge in place. Carefully pull the cartridge straight up and out of the faucet body. Inspect the cartridge's inlet ports for debris and rinse it under water. Also, inspect the inside of the faucet body for any visible sediment and wipe it out with a rag.

If the issue persists after cleaning the aerator and cartridge, the final step is to check the water supply lines and shutoff valves. Place a bucket under the sink. Using two adjustable wrenches—one to hold the faucet's inlet shank steady and one to turn the nut—disconnect the hot water supply line from the faucet. Point the disconnected line into the bucket and slowly open the hot water shutoff valve. If you get a strong stream of water, the valve and line are clear. Close the valve and reconnect the line. Repeat the process for the cold water supply line. If the flow from either supply line is weak, the clog may be in the line itself or the shutoff valve. A faulty shutoff valve may need to be replaced, which is often a job for a professional plumber. After checking, reassemble all components in the reverse order of disassembly. Hand-tighten the sprayer head and supply line connections, then give a slight quarter-turn with a wrench. Turn the water supply back on slowly and check for leaks and improved pressure.