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Low pressure is a symptom with about eight causes, and they separate cleanly once you answer three questions: is it everywhere or one tap, hot or cold, and did it happen overnight or over years? A leak is one of the possible answers, and often not the cheapest one to ignore.
| Pattern | Most likely cause |
|---|---|
| One fixture only, others fine | Clogged aerator, cartridge or a partly closed stop |
| Hot only, whole house | Water heater, scale, or its shut-off not fully open |
| Cold only, whole house | Supply side: main valve, regulator, or the meter |
| Both, whole house, gradual | Scale and corrosion in old galvanised or copper |
| Both, whole house, sudden | A partly closed valve, a failed regulator, or utility work |
| Whole house, and the meter is turning | A supply leak, investigate now |
| Worse when more than one thing runs | Undersized or restricted supply |
| Neighbours have it too | The utility, call the City rather than a plumber |
The bolded row is why this page exists on a leak detection site. Pressure that fell across the whole house alongside a meter that will not sit still is a supply leak until proven otherwise.
Work through that list before spending anything. Between them they account for most low-pressure calls that turn out not to need a plumber at all.
Because a leak is the cause you most want to rule in or out early.
Pressure loss and a moving meter together is one of the clearer diagnoses in this trade. See water leak detection.
A pressure gauge that screws onto a hose bib costs very little and turns an opinion into a number, which changes the conversation entirely.
| Reading | What it suggests |
|---|---|
| Comfortably in the normal range | The problem is flow, not pressure: a restriction somewhere |
| Low at the hose bib | Genuinely low supply: regulator, main valve, or the utility |
| Normal outside but weak indoors | A restriction inside the house, scale, corrosion, a valve |
| High, and you also have weak fixtures | Restriction downstream. See high water pressure |
| It varies a lot through the day | Utility supply variation, or a failing regulator |
The distinction between pressure and flow is the useful one. A restricted line can have perfectly normal static pressure and still deliver a disappointing shower, because the moment water moves the restriction takes over.
If the pressure has faded over years rather than dropped one Tuesday, the pipe itself is usually the answer.
The honest read: gradual whole-house pressure loss in a mid-century house is usually the plumbing telling you its age. See whole house repipe.
Most houses have one where the supply enters, and when it fails it can fail either direction, stuck closed gives you low pressure, stuck open gives you too much.
Detail on both directions of failure is on pressure regulator installation.
We are licensed and insured plumbers, and this site is about leaks, finding the ones you cannot see and repairing them properly. Roughly half of what looks like a plumbing leak turns out not to be one, so the boundary is worth stating plainly.
Roof leaks are a roofer. Water under an air handler is an HVAC technician clearing a condensate drain. Water under an appliance is appliance repair. Drying, restoration and mold are separate trades again, and gas line repair is SoCalGas or a licensed gas fitter. We detect gas leaks, we do not repair gas lines.
The full list, with the trade to call for each, is on what we don’t do.
People use the two words interchangeably and they are not the same thing. Getting them the right way round decides what actually gets fixed.
| Pressure | Flow | |
|---|---|---|
| What it is | Force in a line with nothing moving | How much water actually arrives |
| How it is measured | A gauge on a hose bib, taps closed | Fill a bucket and time it |
| What lowers it | The regulator, the utility, a supply leak | Restrictions, scale, aerators, narrow pipe |
| Complaint it produces | Weak everywhere, consistently | Fine alone, terrible when two things run |
| Typical fix | Regulator, valve, or find the leak | Clean the fixture, or replace the pipe |
The practical test is the shower while somebody flushes a toilet. If it barely changes, your flow is fine and the complaint is pressure. If it collapses, the supply cannot keep up with two demands, and that is a restriction problem no regulator adjustment will solve.
| Sign | What it means |
|---|---|
| Neighbours have the same complaint | Utility supply — call the City, not a plumber |
| It started the day work began in the street | Utility work; usually temporary |
| It is worst at a particular time of day | Peak demand on the local network |
| Water is discoloured as well | A disturbed main. See brown or rusty water |
| It corrected itself after a day | Almost certainly the utility |
The City of Santa Ana’s water line is (714) 647-3380. It is worth one phone call before hiring anybody — if the answer is that they are working on the main two streets over, you have just saved a service call.
A pressure and flow test at multiple points, the regulator checked, the main valve verified fully open, and a meter test to rule a leak in or out. Where the answer is scale in old pipe, you get that plainly rather than a series of partial fixes that never quite work.
Pressure down across the house and a meter that keeps moving is a supply leak.
(714) 386-7923Call or text, day or nightSchedule a VisitSudden loss usually means something changed: a valve knocked partly closed, a failed pressure regulator, utility work in the street, or a significant supply leak. Check the main valve is fully open, then run the meter test.
It can be, and it is worth ruling out first. Pressure that dropped across the whole house alongside a meter that keeps turning with everything off is a supply leak until proven otherwise, and one large enough to affect pressure is not a small leak.
A local problem: a clogged aerator, a worn cartridge, or a supply stop that is not fully open. Unscrew the aerator and rinse the screen first — on hard water that alone fixes a good share of single-fixture complaints.
The water heater or the hot side specifically. Check the heater’s cold inlet valve is fully open, which is a common and free fix. Beyond that, scale inside the tank and on the hot lines builds faster than on the cold side because heat accelerates it.
Usually the pipe. Galvanised steel rusts inward until the bore is a fraction of what it was, and scale builds in copper in hard water. Neither can be cleaned out meaningfully — gradual whole-house loss in an older house is generally a repipe conversation.
A gauge that screws onto a hose bib costs very little. Take a reading with nothing running, then again with a tap open. Normal static pressure with poor delivery means the problem is flow, a restriction — rather than pressure.
Yes. A regulator can fail in either direction, and stuck closed produces exactly this. Pressure that varies through the day with no explanation is a classic sign of one on the way out. They have a service life and are not permanent.
Then it is the utility rather than your plumbing. Call the City of Santa Ana on (714) 647-3380 before hiring anybody — if they are working on a main nearby, you have saved yourself a service call.
Over time, yes. Santa Ana’s supply runs around 250 ppm, and scale builds on the inside of pipes and inside fixture screens. Cleaning aerators and shower heads helps at the fixture; scale inside the lines themselves does not clean out.
Depends what is causing it. An aerator or a half-closed valve, obviously. Scale in old galvanised is worth addressing because that pipe is also going to leak. A supply leak is worth addressing today.