Low water pressure at one faucet? Clean the aerator first

One faucet has gone weak. The kitchen sink used to fill a pot in no time and now it dribbles, or the bathroom faucet sprays sideways and takes twice as long to rinse a razor. Every other fixture is fine. That last detail is the clue: when the problem is at one faucet, the problem is almost always in that faucet, and the first suspect takes five minutes to check.

Remove the aerator

The aerator is the small screened tip screwed onto the end of the spout. It mixes air into the stream, and it catches every grain of sand and flake of scale that comes down the line.

• By hand first. Grip it and turn counterclockwise looking down at the spout, which is clockwise from below. Most come off with fingers.
• Tape-wrapped pliers. If it is stuck, wrap a layer of tape around the aerator or use a rag, then turn it with pliers. Bare metal jaws on a chrome or brushed finish leave permanent marks.
• Hidden cache aerators. Many newer faucets have the aerator recessed inside the spout with no visible knurled edge. Those need a small plastic key that came in the faucet box, or a universal key from the hardware store that has several sizes on one piece. Do not put pliers on the spout itself.

Put the sink stopper in before you start. The aerator comes apart into a housing, one or two screens, a mixer, and a rubber washer, and the small pieces are easy to lose down the drain.

Soak it in vinegar

Take the pieces apart and look. Grit, orange flakes, and white crust are the usual finds. Rinse the loose debris out under the tap, then drop the parts in a cup of white vinegar for an hour, or overnight if the scale is heavy. Scrub the screens with an old toothbrush, rinse, and reassemble in the same order they came apart. Before you screw it back on, run the faucet for a few seconds with the aerator off to flush anything still in the spout. If the flow is strong with the aerator off and weak with it on, you found the problem, and a new aerator is a cheap fix if the old one is badly corroded.

Debris after plumbing or utility work

If the pressure dropped right after something was done to the water, the aerator is where the evidence lands. A water heater replacement, a repair on the main line, a new filtration system, or the utility flushing hydrants on your street all knock loose scale, sediment, and sometimes small pieces of pipe that had been sitting quietly for years. The nearest faucets catch it. Clean every aerator in the house after any of that work, and clean them again a week later, because the first flush does not get everything.

Cartridge and supply stops

If the aerator is clean and the faucet is still weak, the restriction is behind it.

• The cartridge. Inside the faucet body, the cartridge has small passages that scale and grit clog just like the screen does. Turn off the stops under the sink, pull the handle and the retaining clip or nut, lift the cartridge out, and look. Some can be soaked and reused; most are cheap enough to replace with the exact part for the brand.
• The supply stops. The two small valves under the sink may be partly closed, especially if anyone has worked under there recently. Open them fully. On an older stop, the rubber washer inside can also break down and float into the seat, which chokes the flow; that is a stop replacement.
• The supply lines. A kinked flexible line, or an old braided line whose inner tube has collapsed, restricts flow. Replace with a new braided stainless line.

Hot side only versus both

Turn the faucet to full cold, then full hot, and compare.

• Both weak at this faucet only: aerator, cartridge, or stops, as above.
• Hot weak at this faucet only: the hot stop or the hot side of the cartridge.
• Hot weak at every faucet: the water heater. Sediment in a tank heater can block the outlet, a dip tube can fail, or a tankless heater’s inlet screen or heat exchanger is scaled. That is a water heater call, not a faucet call.

When the whole house is low

If every fixture is weak, the faucet is not the problem, and the causes sit upstream.

• Pressure regulator. Many homes have a pressure reducing valve near the meter or where the main enters the house. When one fails it can drop pressure across the house, or let it climb too high. It is a replacement, not an adjustment.
• Main valve partly closed. A house shutoff or the valve at the meter that was closed for a repair or a hurricane and never fully reopened. Gate valves in particular can look open and be half shut. Turn it fully open.
• The meter. A partly closed valve on the utility side, a clogged meter screen, or a utility issue on the street. Check with a neighbor and call the utility.
• A clogged filtration system. A whole-home unit with a neglected sediment prefilter chokes the entire house. Put it on bypass; if the pressure returns, change the filter or service the media.
• Old galvanized pipe. In pre-1970s homes, galvanized steel pipe rusts closed from the inside, and rusty first-draw water is the tell. That is a repipe conversation, not a cleaning.

Aerators, stops that turn freely, and a cartridge are homeowner jobs. Stuck or dripping stops, a regulator, the main valve, a water heater, or galvanized pipe are where to stop: each involves shutting off the house or opening the water heater, and a stop that snaps off at the wall is an emergency at a fixture that was only annoying an hour earlier.

If you have cleaned the aerator and the faucet is still weak, or the pressure is low everywhere, tell us which fixtures, hot or cold, and what changed before it started. We will sort out whether it is the faucet, the heater, or the house.