Low water pressure at one faucet, shower or toilet

Quick answer

If only one fixture is weak, the cause is almost always at that fixture: a clogged aerator or shower head, a half-closed or crusted shutoff valve, or a worn cartridge. If the whole house is weak, look at the main shutoff and the age of the supply pipes.

A lot of Alhambra's houses went up in the 1920s and 1930s, and many still have some original galvanized steel water pipe somewhere in the walls or crawlspace. Over decades, the inside of that pipe builds up rust and scale. Add hard Southern California water, and it is common for one faucet or shower to slowly lose its push while the rest of the house seems fine.

The good news is that a weak single fixture is usually a small, local fix.

First, one fixture or the whole house?

Turn on the kitchen faucet, a bathroom faucet and a hose bib one at a time. If every one of them is weak, the problem is upstream: the main shutoff, a pressure regulator, or the supply pipe itself. If only one is weak, the problem is almost always within a few feet of that fixture.

Quick checks you can do yourself

• Shower heads clog the same way. Soak the head in vinegar overnight, or replace it if the nozzles are cracked.
• Shutoff valves under the sink or behind the toilet are sometimes left partly closed after an old repair. Make sure each one is fully open.
• Hot side only? If only the hot water is weak at one faucet, the cartridge or the hot shutoff is the usual suspect.

What usually causes it in older Alhambra houses

Worn cartridges. Inside most faucets is a cartridge or a set of washers that controls flow. Scale and wear restrict it over time.

Crusted shutoff valves. Old compression stops build up mineral deposits inside, so even when fully open they pass only a trickle.

Old supply lines. Rigid chrome or braided lines from a past remodel can kink or narrow inside.

Galvanized pipe near the fixture. When a short run of old galvanized pipe feeds one bathroom, scale can choke it down. Replacing a short section near a fixture is sometimes reasonable; a whole-house repipe is a bigger project for a plumbing contractor.

Start at the aerator

When only one faucet is weak, the problem is almost always at that faucet. Unscrew the aerator from the tip of the spout, using a cloth on pliers if it is tight. Look for grit, scale and flakes of rust.

In older Alhambra homes with galvanized pipe, small rust flakes break loose whenever water is shut off and turned back on, and they collect in aerators. Rinse the screen, soak it in vinegar if it is scaled, and reinstall it. If you cannot clean it, replacements are inexpensive; bring the old one to match the thread size.

Cartridges and stems

If the flow is still weak with the aerator off, the restriction is inside the faucet. Single-handle faucets use a cartridge that can clog with sediment. Two-handle faucets use stems with washers, and on old faucets those washers can swell and partly block flow.

Turn off the shutoffs, remove the handle and pull the cartridge or stem. Flush the faucet briefly into a bucket with the cartridge out, then clean or replace it.

Check the shutoff valve

Old multi-turn shutoff valves under sinks sometimes do not open fully, or their internal washer breaks apart and blocks the opening. Open the valve all the way by turning it counterclockwise. If it barely turns or flow stays low, the valve may need replacing.

Supply lines

Old chrome or plastic supply tubes kink or clog. A kinked line restricts water, and an old line can also burst. Braided stainless supply lines are a cheap upgrade.

Showers and tubs

Low pressure at one shower can come from a clogged shower head, a worn cartridge, or a stop built into the valve. Soak the head in vinegar overnight. If both the tub spout and shower are weak, the valve is likely the issue.

Hot only or cold only

If only the hot water is weak at one faucet, the hot cartridge side or valve may be clogged. If hot is weak everywhere, the water heater may be full of sediment or its valve partly closed.

Galvanized pipe

When several fixtures are weak, especially at the far end of the house, the galvanized pipes may be clogged inside with rust. That is a bigger job. Replacing galvanized pipe, often with copper or PEX, restores pressure and reduces rust in water.

We can look at the pipe and tell you what we find before suggesting a repipe. See replacing faucets on vintage sinks if you want a new faucet while fixing the flow.

What our visit involves

We test the flow at the fixture, then work backward. We clean or replace the aerator or shower head, swap the faucet cartridge if it is worn, and replace crusted shutoff valves and supply lines with new quarter-turn stops and braided lines. Before we leave, we run every fixture we touched and check each connection for drips.

See our faucet repair and under-sink leak repair pages for more.

If we find that the weak spot is buried in the wall or the whole house is starved, we tell you plainly what we found so you can decide on next steps.

Keeping pressure up

Clean aerators and shower heads once or twice a year. Open and close every shutoff valve once a year so they do not seize. And if you are already doing a bathroom update, that is the right time to replace the old stops and lines behind it.

When a pressure call lands near Main Street, we usually fit in a quick dim sum lunch at Lunasia before the next house.

Want us to handle it?

Call or text (626) 684-3505, Mon–Sat 8:30 AM–7 PM. Send a photo and we will give you an upfront quote.

Call or text (626) 684-3505