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. The good news is that most causes are findable, and a fair number of them you can check yourself before anyone touches a wrench.
This is a homeowner’s guide to what’s actually going on behind the wall. We don’t do plumbing work and we’re not a contractor. The goal here is to help you understand the problem so you can fix the simple stuff and know when it’s time to bring in a pro.
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 the easy wins, and they’re 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 a likely suspect.
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 failing regulator is one of the most common whole-house culprits, and it’s not a DIY swap for most people.
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, and some have early copper too. 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.
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 much of the 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.
If the pressure’s low across the whole house and you’ve ruled out the simple stuff, that’s the point to bring in a pro. The same goes for a suspected bad regulator, signs of galvanized pipe rusting shut, or any pressure problem you simply can’t trace. A plumber can measure your actual psi, test the regulator, and look at your pipe material to tell you what’s really going on.
Before you hire anyone, verify their license. In California, plumbing contractors are licensed by the CSLB, and you can check any license for free at cslb.ca.gov to confirm it’s active and in good standing. It takes a minute and it’s the simplest way to protect yourself.
Low pressure is rarely a mystery once you know where to look. Start at the faucet, work your way back toward the street, and you’ll usually find the pinch.