You turn on the shower and it’s a trickle. The kitchen faucet takes forever to fill a pot. Low water pressure is one of those everyday annoyances that’s easy to live with and easy to misdiagnose. Most causes are findable, and a few checks take five minutes.
This is an information guide. We don’t do plumbing work and we’re not a contractor. The goal is to help you understand what’s going on so you can handle the simple checks yourself and know when it’s time to call a licensed plumber.
First question: everywhere, or just one spot?
This single question narrows things down fast.
If the weak water shows up at one faucet or one shower, the problem is almost always local to that fixture. If it’s low all over the house, you’re looking at something shared: a valve, a regulator, or the supply coming in from the street.
Walk around and test a few taps, hot and cold, on different floors if you have them. Note what you find. That five-minute check tells you which half of this article matters for you.
Single-fixture problems
These are worth ruling out first because they cost nothing to check.
Clogged aerator. That little screened tip on the end of most faucets catches grit, rust flakes, and mineral bits. Across much of the Bay Area, hard water is the norm, so these screens scale up faster than you’d think. Unscrew the aerator by hand or with pliers and a rag, rinse the screen, soak it in vinegar if it’s crusty, and reinstall. This fixes more “broken faucets” than almost anything else.
Gunked-up showerhead. Same story. The tiny nozzles clog with scale. Soak the head in white vinegar for a few hours, scrub the holes with an old toothbrush, and you’ll often get your shower back.
A partly closed angle stop. Under sinks and behind toilets there’s a small shutoff valve. If someone bumped it or closed it partway during a repair, that fixture runs weak. Make sure it’s open all the way.
A failing fixture cartridge. Single-handle faucets have a cartridge inside that can wear or clog. If the aerator’s clean and the valve’s open but that one faucet is still weak, the cartridge is likely the cause. Replacing a cartridge means disassembling the handle and sourcing the right part. That’s a job for a licensed plumber.
Whole-house problems
When the pressure’s low everywhere, the cause is upstream of your fixtures.
A pressure regulator going bad. Most Bay Area homes have a pressure-reducing valve (a PRV) near where the main line enters, often by the front hose bib or in the garage. It’s a bell-shaped brass fitting. Its job is to knock the street’s high pressure down to a house-friendly level. These parts wear out, usually somewhere in the 10-to-15-year range, and when they fail they can drop your pressure across the whole house. A PRV swap is not a DIY job. Call a licensed plumber.
A main shutoff that isn’t all the way open. Your home’s main valve, and the one at the meter, should be fully open. After any plumbing work, a valve sometimes gets left partly closed. An older gate valve can also fail internally, with the inside stem breaking off so the valve “feels” open but isn’t. Worth a look.
Galvanized pipe rusting shut. This one’s a Bay Area classic. Plenty of older homes in the East Bay and Tri-Valley still have galvanized steel supply pipe. Galvanized rusts from the inside, and over decades the rust narrows the opening until water can barely squeeze through. The telltale sign is pressure that’s been slowly fading for years rather than dropping overnight, often worse at upstairs or far-end fixtures. If your house was plumbed before the 1960s and never repiped, this deserves serious consideration. A plumber can assess the pipe and tell you what you’re dealing with.
Hard water scale in general. Beyond the fixtures, mineral buildup slowly coats the inside of valves, water heaters, and pipe over time. It’s a gradual squeeze rather than a sudden block, but in a region with hard water it adds up.
A water softener or whole-house filter clogging. Softeners are everywhere here because of the hard water, and their resin beds and valves can restrict flow as they age. Whole-house sediment filters do the same when the cartridge fills up. If you’ve got either one, check it. Many softeners have a bypass you can flip to test whether it’s the bottleneck.
Supply from the street. Sometimes it’s not your house at all. Utility work on the mains can drop pressure or push sediment into your lines, and your water provider, whether that’s EBMUD, Cal Water, or a Tri-Valley city system fed by Zone 7, can tell you if there’s a known issue or what static pressure they deliver to your area.
A note for East Bay homeowners
If you’re buying or selling in the inner East Bay, you may run into the EBMUD Private Sewer Lateral program, which requires testing and, if needed, repairing the sewer lateral at point of sale. That’s the sewer side, not your supply pressure, so it won’t fix a weak shower. But it’s a reminder that older underground plumbing in this region is often near the end of its life, and the same age that wears out a lateral is the age that rusts galvanized supply pipe shut.
When to call a licensed plumber
Do the free checks first. Clean your aerators and showerheads. Confirm your shutoff valves are fully open. Test your softener bypass if you have one. A surprising share of low-pressure complaints end right there.
Anything past those basic checks needs a licensed plumber. A bad regulator, galvanized pipe, a worn cartridge, an internal valve failure. None of those are jobs to guess at. A plumber can measure your actual psi, test the PRV, and look at your pipe material to tell you what’s actually going on and what it’ll take to fix it.
Before you hire anyone, verify their license at cslb.ca.gov. California plumbing contractors are licensed through the CSLB, and checking takes about a minute. An active license means they’re accountable; no license means no protection if something goes wrong.
Low pressure is rarely a mystery once you know where to look. Start at the faucet, work your way toward the street, and when the simple checks don’t solve it, get a licensed plumber involved.